Physics

Physics Overview

Physics and its Branches

The term Science is derived from the latin word, Scientia which means 'know'. Physics is a branch of science deals with the study of matter and energy. The goal of physics is to comprehend the nature of matter and the reasons behind its behavior. It is the study to understand how energy is created, how it moves, and how it may be managed. The relationship between matter and energy, as well as how they influence one another over time and space, are other topics of interest to physicists. The Greek word for "physics" means "natural things." Semi-conductor devices, including the transistor, were created by solid-state physicists. The electronics sector grew significantly as a result of these devices. Astronomy, biology, chemistry, geology, and other sciences all benefit from knowledge gained by studying physics. Additionally, physics and real-world advancements in engineering, health, and technology are closely related. Physics is the first branch of science developed by man based on the motion of stars and celestial bodies. Modern physics and Classical physics are the two main branches of physics.

Classical Physics

Refers to the traditional physics that was identified and developed before the 20th century. The main branches are given below.

1. Classical Mechanics - The study of force exerted on an object in motion or at rest. Mechanics is the field of physics that studies the effects of forces on solids, liquids and gasses at rest or in motion. Mechanics can be divided into two branches - statics and dynamics. Statics studies bodies at rest or in motion at a constant speed and in a constant direction. Dynamics is the study of bodies that undergo a change of speed or direction or both, when forces act upon them. Kinematics and Kinetics are the two branches of Dynamics.

2. Thermodynamics - Thermodynamics is the study of various forms of energy, such as heat and work and of the conversion of energy from one form into another.

3. Optics - Optics is the branch of physics and engineering that is concerned with the properties of light. It describes how light is produced, how it is transmitted and how it can be detected, measured and used.

4. Electricity and Magnetism - The study of electricity and magnetism and their interrelationships.

5. Acoustics - It is a branch of classical physics that deals with the study of sound, including its production, transmission, and effects.

6. Astrophysics - Astrophysics is a branch of physics that studies the physical and chemical structure of stars, planets, and other objects in space.

7. Relativity - One of the branches of theoretical physics, the study of the interrelationship of space, time, and energy when an object is in motion.

Modern Physics

Refers to a concept in physics that has emerged since the beginning of the 20th century.

1. Quantum Mechanics - Quantum Mechanics is a branch of physics that describes the nature, structure, phenomenon and motion of the atomic and sub atomic particles.

2. Atomic Physics - The branch of science that studies the structure and properties of atoms.

3. Nuclear Physics - Nuclear Physics is the branch of modern physics that deals with the study of properties, structure and reactions of atomic nuclei.

4. Condensed Matter Physics - This field of science includes the study of the properties of condensed matter, the developing fields of nanoscience, and photonics as subfields.

5. High Energy Physics - High Energy Physics or particle physics, is a branch of physics that focuses on the fundamental constituents of matter and radiation, and the forces that govern their interactions.

6. Electronics - Electronics is the branch of physics and engineering closely related to the science of electricity. It is the study of nature, control and application of electrons.

States of Matter

Matter is the substance of which all things are made. All objects consist of matter. The objects may differ widely from one another. But they have one thing in common, that they all occupy space. As a result, anything that takes up space is typically considered matter by scientists. All matter has inertia. This means that it resists any change in its condition of rest or of motion. An object's mass is the amount of matter it contains. but scientists usually prefer to define a mass as a measure of inertia. The earth's gravitational attraction for a given mass gives matter its weight. The farther an object travels from the earth's center, the less gravity pulls on it. For this reason, objects that move from the earth into outer space lose weight even though their masses remain the same. Any object that requires space to exist and has weight is generally called matter. Matter has seven main states.

1. Solid

One of the three possible states of matter is referred to as a solid. The other states are liquid and gaseous. The state of each body of matter is classified according to the power of its molecules to resist forces that may change its shape. A solid has a fixed shape and volume because its molecules cannot move freely.

2. Liquids

Substances that have no definite shape, have a definite volume, and can take on any shape.

3. Gases

Gases are substances that have no definite shape or volume and the distance between their molecules is very large.

4. Plasma

Plasma in physics is a form of matter composed of electrically charged atomic particles. Plasma makes up the sun, other stars, and the majority of other celestial bodies. Lightning bolts also consist of plasma, few other plasma occurs naturally on the earth. Artificially created plasmas have many practical uses. Electricity, for instance, transforms the gas in a neon sign's tube into plasma that emits light. A welding process called arc welding uses electricity to produce the high temperatures needed to join pieces of metal. In the future, plasma fuels may be used by electric rockets to make lengthy space voyages. Plasma can be made by heating a gas or by passing an electric current through it. It is the fourth state of matter.

Examples of Plasma

• The state in which matter is most abundant in the universe.

• The state in which matter is found in the center of the sun and stars.

• The reason for the glow of the sun and stars.

• Plasma is created in stars due to very high temperatures.

• In the plasma state, particles are found in a super energetic / excited state.

• Plasma is found in fluorescent tubes and neon sign bulbs.

• The state in which molecules are found in the most disordered state.

• The state in which matter reaches very high temperatures.

• The state of matter in which substances exist in an ionized state at high temperatures.

• The state in which matter is found in lightning.

• A group of free charged particles.

5. Bose - Einstein Condensate

A Bose - Einstein Condensate is a state of matter that results when a gas of bosons is cooled to a temperature very close to the Kelvin by subjecting it to an external potential. The Bose - Einstein Condensate was predicted by scientists Satyendranath Bose and Albert Einstein. In 2001, Eric A Cornell, Wolfgang Ketterle, and Carl.E.Weimann were awarded the Nobel Prize for their work on Bose-Einstein condensates in dilute gases of alkali atoms and for their early studies of the properties of condensates. It is the fifth state of matter.

6. Fermionic Condensate

A Fermionic Condensate is a state of matter formed by the aggregation of Fermionic particles at low temperatures. The first atomic fermionic condensate was discovered by a team led by Deborah S. Jin using potassium-40 atoms in 2003. It is the sixth state of matter.

7. Quark - Gluon Plasma

Quark - Gluon Plasma is a state of matter at very high temperatures. Quarks are the fundamental elementary particles found in all matter in the universe. The quark model was independently proposed by physicists Murray Gell-Mann and George Zweig in 1964. Hadrons are particles made up of quarks. It is the seventh state of matter.

Newly discovered states of matter

1. Time Crystal

A time crystal is a man-made state of matter appears to remain in perpetual motion without taking in any energy - which should be impossible.

2. Excitonium

Excitonium is a condensate that exhibits the macroscopic quantum phenomena, such as a superconductor, superfluid or insulating electronic crystal.

3. Rydberg Matter

Rydberg Matter is a material made up of excited atoms. At a certain temperature, these atoms split into ions and electrons.

4. Jahn–Teller Metal

In 1937, scientists Arthur Jahn and Edward Teller reported on Jahn–Teller Metal. The presence of Jahn–Teller Metal was discovered in an experiment using rubidium atoms at temperatures close to absolute zero. Jahn–Teller Metal is a material formed from the unique chemical bonding of atoms in a molecule called Buckminster fullerene, which is made up of carbon 60 atoms. Fullerides are molecules made by transferring other atoms to fullerene molecules, which only contain carbon atoms. Jahn–Teller Metal acts as an electrical conductor and an electrical insulator at the same time. Jahn–Teller Metal is a state where metal, magnetism, insulator, and superconductivity come together. Jahn–Teller Metal exhibits superconductivity even at the highest temperatures. Jahn–Teller Metal is the ninth state of matter.

5. Quantum spin liquid

A quantum spin liquid is a material with a two-dimensional structure similar to graphene. In this material, electrons are in the Majorana fermion state. Majorana fermion is a state in which electrons are both particles and antiparticles at the same time. In magnetic materials, electrons behave like bar magnets. In this state, electrons do not behave like bar magnets even when the temperature is reduced to absolute zero.

6. Chain melted state

The Chain melted state is a state of matter discovered by scientists at the University of Edinburgh. The Chain melted state is a state in which atoms in a substance appear as solids and liquids at high pressures and temperatures.

Units and Measurements

The chosen standard used for measuring a physical quantity is called unit. Units are of two types - Fundamental Units and Derived Units.

Fundamental Units - The physical quantities which do not depend upon other quantities are known as Fundamental Quantities. Fundamental Units are the units of fundamental quantities.

Derived Units - Many units have also arisen from the basic/fundamental units. These are the 'derived units'. All the units which are defined or expressed in terms of fundamental units are called Derived Units. Several Systems of unit have been in use for describing measurement. The common systems are the C.G.S system based upon basic units such as centimetre, gram and second. F.P.S system (foot, pound, second) which is the British system. M.K.S system based upon basic units such as metre, kilogram and second.

S.I units – S.I units is the modified form of M.K.S system. System of International units, abbreviated as S.I units is the internationally accepted system. Today, the SI unit is accepted as the basic unit throughout the world. SI units began to be used worldwide in 1960. Various measurements in the scientific world are presented in SI units. In this system there are seven fundamental units and three supplimentary units. The seven fundamental units are metre, kilogram, second, ampere, kelvin, candela, mole. radian and sterdian are supplementary units.

Fundamental Units (Quantity, SI Unit & Symbol)

■ Length - metre (m)

■ Mass - kilogram (kg)

■ Time - Second (s)

■ Temperature - kelvin (K)

■ Electric Current - ampere (A)

■ Luminous Intensity – candela (cd)

■ Unit of Particle – mole (mol)

Supplementary Units (Quantity, SI Unit & Symbol)

■ Plane Angle – radian (rad)

■ Solid Angle – sterdian (sr)

Important Derived Units (Quantity, SI Unit & Symbol)

■ Force - newton (N)

■ Distance and Displacement - metre (m)

■ Velocity and Speed - metre/second (m/s)

■ Acceleration - metre/second² (m/s²)

■ Pressure - newton/metre, pascal (Pa)

■ Work and Energy - joule (J)

■ Power - watt (W)

■ Frequency - hertz (Hz)

■ Intensity of Sound - decibel (dB)

■ Intensity of Electric Field - newton/coulomb (N/C)

■ Intensity of Magnetic Field - tesla (T)

■ Potential Difference - volt (V)

■ Electric Charge – coulomb (C)

■ Electric Conductance - siemens (S)

■ Electric Current – ampere (A)

■ Electric Resistance - ohm (Ω)

■ Electric Capacitance - farad (F)

■ Resistivity - Ohm metre (Ωm)

■ Radio Activity - curie, rutherford, becquerel (Bq)

■ Distance of Stars - light year (ly)

■ Power of Lens - dioptre (dpt or D)

■ Illuminance - lux (lx)

■ Inductance - henry (H)

■ Magnetic Flux – weber (Wb)

■ Wave Length - metre (λ)

■ Area - square metre (m²)

■ Volume – cubic metre (m^-3)

■ Speed – metre per sec (ms^-1)

■ Momentum – kg metre/sec (kgm/s)

■ Power of Machines – horse power (hp)

Units of Length in Metre

■ 1 millimetre (mm) - 10^-3 metre

■ 1 centimetre (cm) - 10^-2 metre

■ 1 Micron (µm) - 10^-6 metre (Microns is the unit of distance defined in terms of micrometre. Used commonly in Biology)

■ 1 nanometre (nm) - 10^-9 metre (used by optical designers)

■ 1 Angstrom (A°) - 10^-10 metre

■ 1 Astronomical Unit (AU) – 1.496 x 10¹¹ metre (It is another unit of distance in space. It is the mean distance between earth and sun. One light year contains nearly 63282 Astronomical Units)

■ 1 Light Year - 9.46 x 10¹⁵ metre (Light Year is the distance travelled by light in vacuum in one year at a speed of 3 x 10⁸ m/s. Light Year is a unit of distance used in astronomy.)

■ 1 Par sec (parallactic second) - 3.08 x 10¹⁶ metre or 3.26 Light Year (The largest unit of Distance is par sec)

Conversion of Units

■ 1 Nautical Mile - 1.852 kilometre

■ 1 Mile - 1.60 kilometre

■ 1 Yard – 0.91 metre

■ 1 Feet – 0.3 metre

■ 1 Inch - 2.54 centimetre

■ 1 Horse Power – 746 watt

■ 1 Pound - 0.454 kilogram

■ 1 Square feet – 0.09 square metre

■ 1 Acre – 10⁴ square metre

■ 1 Hectre - 2.471 Acre

■ 1 Litre – 1000 cubic cm

■ 1 Ounce – 28.35 gram

■ 1 Gallon - 4.546 litre

■ 1 Barrel - 159 litre

■ 1 Feet – 12 inch

■ 1 Yard - 3 feet

■ 1 Mile – 5280 feet

■ 1 Nautical Mile – 6080 feet

■ 1 Fathom – 6 feet

■ 37° Centigrade – 98.6° Fahrenheit

■ 32° Fahrenheit - 0° Centigrade

■ 60 seconds - 1 minute

■ 60 minutes – 1 hour

■ 90° - Right Angle

■ 180° - Semi Circle

■ 360° - Circle

Temperatures

A thermometer is used to measure ambient temperature and is filled with mercury. The three units used in thermometers are Celsius, Fahrenheit, and Reaumur. According to the Celsius system, water freezes at zero degrees Celsius and boils at 100 degrees Celsius. According to the Fahrenheit system, water freezes at 32 degrees Fahrenheit and boils at 212 degrees Fahrenheit.

■ -273°C - The lowest temperature that can be reached is absolute zero.

■ -230°C - The temperature of Pluto's atmosphere.

■ -89.2°C - The lowest temperature ever recorded on Earth (in Antarctica).

■ -39°C - Mercury turns solid.

■ 0°C - Water freezes

■ 4°C - Maximum density of water

■ 36.8°C - Human body temperature

■ 37°C - Optimum temperature for egg hatching

■ 41°C - Body temperature of birds

■ 58°C - Highest temperature ever recorded on Earth (in Libya)

■ 100°C - Water boils

■ 250°C - Wood catches fire

■ 500°C - Optimum temperature used in ammonia production

■ 600°C - When cooking gas burns

■ 1063°C - Melting point of gold

■ 3410°C - Melting point of tungsten

■ 5500°C - Temperature of the surface of the Sun

■ 16 Million°C - Temperature at the center of the Sun

Units

■ Rainfall measurement unit - centimeter

■ Length measurement unit - meter

■ Area measurement unit - square meter

■ Radioactivity measurement unit - curie

■ Luminous intensity measurement unit - candela

■ Magnetic field strength measurement unit - tesla

■ Force measurement unit - newton

■ Resistance measurement unit - ohm

■ Pressure measurement unit - pascal

■ Power measurement unit - watt

■ Energy measurement unit - joule

■ Electric current measurement unit - ampere

■ Frequency measurement unit - hertz

■ Potential difference measurement unit - volt

■ Electric charge measurement unit - coulomb

■ Capacitance measurement unit - farad

■ Wavelength of light Unit of measurement - Angstrom

■ Unit of distance in space - Light year

■ Unit of power in machines - Horsepower

■ Unit of expansion - Cubic meter

■ Unit of distance to stars - Light year

Motion - Laws of Motion, Types and Examples

If the position of an object in space changes with time relative to an observer, it is said to be in motion. Motion occurs when an object change its location in space. Motion is a relative rather than an absolute term. An object may be in motion with regard to another object, but may be stationary with respect to a third object. For example, suppose you are riding on a train and you pass a person standing alongside the tracks. The person standing along the tracks will see you and everyone else on the train as being in motion. But the person sitting next to you on the train will be stationary with respect to you. Everything in the universe is in motion. Even as you sit reading a book, you are moving very rapidly because the earth is rotating its axis. You are also moving with the earth as it revolves around the sun. In addition, the sun, the earth and the rest of the planets in our solar system are involved in the general rotation of our galaxy within the universe.

We cannot imagine a state of motionlessness. Force and motion are related to each other like two sides of a coin. If any object is moving, there is definitely a force behind it. What if we want to make a moving object stand still? A force will have to be applied there too. The motion of objects is the most common phenomenon in nature. All physical phenomena are related to motion. The scientific basis for the study of motion was provided by scientists such as Galileo, Kepler and Newton. The laws which govern the motion of bodies were discovered by the scientist Sir Issac Newton.

Physical Quantities

Physical Quantities are of two types – Scalar and Vector Quantities. Scalar Quantities have only magnitude and no direction. For Example - Distance, Mass, Temperature, Speed etc. Vector Quantities have both magnitude and direction. For Example – Displacement, Weight, Velocity, Acceleration etc.

Distance and Displacement

The actual length of path travelled by a body is called the distance covered by a body. The shortest distance from the initial to the final position of a body is called displacement of the body. It does not depend on the actual path undertaken by the object. It has a direction and a magnitude. Its unit is the meter (m). When describing displacement, it is complete only if the direction is also indicated along with the distance traveled. Physical quantities that require a direction along with a magnitude are called vector quantities. Physical quantities that do not require a direction are called scalar quantities. Like ordinary numbers, vectors can be added, subtracted, multiplied, and divided. When an object moves in the same direction along a straight line, its distance and displacement are equal.

Speed and Velocity

The rate of change in position of objects when a force is applied is called speed. If this change in position occurs in a particular direction, it is called velocity. As a ball thrown into the sky falls, its velocity increases. This happens because the gravitational force of the Earth continuously acts on it.

Speed: Speed ​​is the distance travelled by a body in unit time. It is a scalar quantity. The basic SI unit of speed is meters/second or kilometers/hour.

Speed ​​= distance travelled by the object/time travelled by the object

If an object travels equal distances in equal interval of time, its movement is at the same speed. It is called uniform speed. If the object travelled different distance in equal (similar) time intervals then it is referred to as non-uniform speed. A speedometer is an instrument that measures the speed of a vehicle.

Velocity : Velocity is the displacement per unit time. Velocity is the rate at which a body moves in space in a given direction. Velocity is expressed in distance and time, such as metres per second. The distinction between velocity and speed is significant. Although it doesn't provide anything about the direction of motion, speed does reveal the rate of motion. When a body is said to have a speed of 40 kms per hour, the direction is unknown. To specify the velocity, it is necessary to indicate both the rate and the direction of motion. For example, a body may have a velocity of 40 kms per hour toward the north. Mathematically, velocity is a vector quantity, because it has both speed and direction.

The basic SI unit of velocity is - meter/second or kilometer/hour.

Velocity = displacement/total time taken to travel

When the amount of displacement of an object is equal at equal intervals and is moving in the same direction, the velocity of that object is uniform. If the direction and speed of an object are changing, the velocity of that object is non uniform.

Acceleration and Retardation

Acceleration

Acceleration is the rate of change of velocity. It is a vector quantity. Imagine a stone tied to a string spinning in a circle. Although the speed is the same, the direction of the stone changes every moment. As the direction changes, the velocity also changes. The change in the velocity of an object in a given time is called acceleration. The scientist who proposed the concept of acceleration was Galileo Galilei. Acceleration is the change in velocity per unit time. That is, the term acceleration refers to the increase in velocity. The basic unit of acceleration is meters/second squared. Acceleration is a vector quantity.

Acceleration = Change in Velocity/Time = (v - u) / t

v = final velocity, u = initial velocity, t = time interval

If the acceleration remains constant, i.e, it does not change with time it is said to be uniform acceleration.

Retardation

A decrease in the velocity with time is called deacceleration or retardation. If the acceleration is negative, it is called deceleration or negative acceleration.

Projectile and Trajectory

Projectile is the name given to a body which after having been given an initial velocity is allowed to move under the influence of gravity alone. The path of the projectile is called trajectory. The trajectory of a projectile moving under the influence of a constant acceleration is a parabola. A projectile has maximum range when the angle of projection is 45°.

Types of Motion

1. Linear Motion

If an object moves in a straight line, it is called Linear Motion. If this motion is at a constant speed, it is called Uniform Linear Motion. The object travels the same distance in a given time. Non-Uniform Linear Motion is linear motion that is not at a constant speed.

Example of Linear Motion - A mango falling suddenly

2. Circular Motion

Circular Motion is a motion in which different parts of a body move around a central fixed point or axis in a circular path with different radii. The movement of an object along a circular path is called 'Circular Motion'. The Earth's rotation around the Sun, the movement of a pencil when drawing a circle using a compass, the movement of a clock's needle, and the movement of a stone when a string is tied to it are all examples of circular motion.

3. Rotatory Motion

When an object moves, the centers of the circles drawn by each point on it lie on the same line. This line is the axis of the circle. Rotational motion is when an object rotates on its own axis.

Example: The earth rotating on its own axis, a rotating chair, a rotating drum, a small wheel in a sewing machine, wheels in a powder mill, the motion of a spinning wheel, the motion of the blades of a rotating fan

4. Revolutionary Motion

Orbit is the motion of a rotating object that is outside the axis of the object.

Example: The annual motion of the Earth around the Sun

5. Projectile Motion

When an object is thrown or launched and is in flight, it is called a projectile. A football, a cricket ball, or a baseball can all be projectiles. Projectile motion can be thought of as the result of two separate and simultaneous forces. The acceleration experienced by the object after launch is due to gravity. Moreover, it is experienced vertically downward. "The limits of projectiles known as two different slopes equal to or less than 45° are equal". The initial energy and, consequently, momentum of the launched projectile are lost due to forces such as friction, viscous force, and air resistance. Thus, the projectile travels a parabolic path and falls to the ground.

6. Translatory Motion

It is a motion in which every part of a body moves in the same direction by an equal distance at the same time. For Example – Moving vehicles like cars, buses, trains

7. Rectilinear Motion

It is a motion along a straight line. Example – The up and down movement of lifts.

8. Curvilinear Motion

Curvilinear Motion is a motion along a curved path. Example – The motion of a rocket in space.

9. Oscillatory Motion

It is a motion in which a body moves back and forth about its mean position. All vibratory motions are oscillations.

Examples: The motion of the pendulum in a pendulum clock, a simple pendulum, the motion of a hanging lamp, the motion of ocean water as ocean waves pass by, the movement of a swing.

10. Periodic Motion

It is a motion which repeats itself after a fixed interval of time. All oscillatory motions are periodic motions. Example – The rotation of the earth around the sun.

Dimensions of Motion

One Dimensional Motion – If the motion of an object is restricted to a straight line, it is an one dimensional motion. Example – Train running along a straight track.

Two Dimensional Motion – If the motion of an object is restricted to a plane, it is a two dimensional motion. Example – motion of a boat on a lake, a coin along a surface, motion of projectiles, motion of satellites, motion of charged particles in electric and magnetic fields.

Three Dimensional Motion – An object moving in space is said to be in three dimensional motion. Example – A butterfly flying in air or motion of gas molecules in space.

Momentum

Momentum is defined as the product of mass and velocity of a body. In physics, Newton defined momentum as a moving body's amount of motion. When a cricket bat is swung, it has a momentum that depends on its mass and how fast it moves. The force exerted on the ball when the ball hits it depends on the rate of change in the bat's momentum. Any moving object's momentum can be calculated by multiplying its mass by its velocity.  If a car has a mass of 1000 kilograms, when driving north at 5 metres per second, it has a momentum of 5000 kgm metres per second toward the north. To have the same momentum as the car, the truck having mass of 5000 kilograms, must drive north at only 1 metre per second. Momentum is a vector quantity.

If Mass = 'm' and velocity = 'v'

Then, Momentum = Mass x Velocity, i.e, P = mv

Unit of Momentum = kgm/s

Inertia

Inertia is the tendency of a body to continue in its state of rest or the state of uniform motion along a straight line. Inertia is a property of all matter. It makes an object that is not moving continue motionless unless some force puts it into motion. Inertia also makes a moving object continue to move at a constant speed and in the same direction. Unless some outside force changes the object's motion. A moving item can only be made to slow down, speed up, stop, or turn by such a force. One force that commonly slows or stops a moving object is friction with other objects. The force required to change an object's motion depends on the mass of the object. The quantity of matter that makes up a thing is its mass. The greater an object's mass, the harder it is to put the object into motion or to change its direction or speed.

Inertia of Motion

Inertia of Motion describes the inability of an object to change its state of motion on its own.

Examples of Inertia of Motion

■ A fan continues to spin for a short time even after being switched off.

■ An athlete runs some distance before taking a long jump, by running the athlete gives himself larger inertia of motion.

■ A running athlete cannot stop running as soon as he reaches the finishing line.

■ A person standing on a fast-moving bus, falls forward suddenly when brakes.

Inertia of Rest

Inertia of Rest describes the inability of an object to change its state of rest on its own.

Examples of Inertia of Rest

■ As the train starts moving, a man sitting inside leans backwards because of inertia of rest.

■ The ability to drop the bottommost coin of a stack of carrom coins on a carrom board without disturbing the stack.

■ The mango falls when the mango branch is shaken suddenly.

■ The passengers in the bus lean backwards when a stopped bus suddenly moves forward.

Torque

The amount of twisting effort applied to an object by a force or forces is known as torque. Multiplying the force by the distance between the axis and the line of force yields the torque around any axis. The torque increases as the force moves farther from the axis. For this reason, a wheel turns more easily when the force is applied farther from the centre. Torque (Moment of Force) is a vector quantity.

Symbol of torque : τ

τ = rF sinθ

r = Position vector

F = Force

θ = Angle measurement

Impulse

Impulsive Force is the application of a large force for a short period of time. For example, the force applied when hammering a nail. The total effect of a force on an object is called impulse. The momentum and momentum difference of a force experienced by an object are equal. This is the Impulse Momentum Principle.

Impulse Force = Force x Time

Equations of Motion

There exists some relation between velocity, acceleration, and the time intervals during which we study the motion of a body. These relations are called equations of motion.

They are : v = u + at

s = ut + ½at²

2as = v² – u²

Where, v = final velocity, u = initial velocity, t = time interval, a = acceleration and s = displacement.

Newton’s Laws of Motion

First Law – Every body continues in its state of rest or uniform motion in a straight line unless compelled by an external unbalanced force.

Second Law – The rate of change of momentum is directly proportional to the external unbalanced force and takes place in the direction of the force.

F = ma, where F = Force, m = mass, a = acceleration

Third Law – To every action, there is an equal and an opposite reaction. Action and reaction are equal and opposite but they never cancel each other as they act on different objects.

Examples of Third Law – The flying of birds, Swimming, Rocket working (Newton’s third law and law of conservation of linear momentum), firing of gun (When a shot is fired from a gun, the gun recoils due to the reaction force applied by the shot on the gun)

Force - Definition, Units, Types

Force is any influence that changes or tends to change the state of rest or the uniform motion in a straight line of a body. Mechanical force is the force associated with motion. The strongest force in nature is nuclear force and the weakest force in nature is gravitational force.

Unit of force is Newton (N) in SI Unit. Dyne (CGS Unit) is yet another unit of force.

One Newton = 100000 dynes

Newton’s second law gives the measure of force.

i.e., F = ma ; F – Force, m – mass, a – acceleration

Fundamental Forces

There are four fundamental forces in the universe. They are gravity, the strong nuclear force, the weak nuclear force, and the electromagnetic force. Of these, gravity and the electromagnetic force have long-range limits. The other two act at short distances.

Contact and Non Contact Forces

All objects in the universe are subject to the force of some other object. We can mainly divide forces into two types: contact force and non-contact force. Contact force is the force that occurs between two objects that are in contact with each other. Weight, Normal Force, Frictional Force, Te​nsion, Spring Force are examples of Contact forces. Non-contact force is the force that occurs between objects that are not in contact with each other. Gravitational Force, Electrostatic force, Magnetic force are examples of Non Contact Forces.

Types of Forces

1. Normal force

Imagine a book on a table. The gravitational force of the earth is always pulling it down. But the book does not fall down. The table supports it. This is an example of normal force. Take two bricks and put a scale on top of them. You can put a small stone on this scale. The scale will bend down a little. But you can see that it supports the stone. This is also due to normal force. If you press the scale down with your hand, you can feel this force exerted by the scale.

2. Weight 

Weight is the gravitational force exerted by the Earth on an object. Weight can be defined as the force gravitational acting on a body. Mass remains constant while weight varies from place to place.

Weight, w = m x g

3. Impulsive Force

Impulse of a force is the product of the force and the time during which the force acts on the body. The large force acting for a very short time is called an impulsive force. It is measured as the rate of change in momentum. For example, force exerted on a bullet when it is fired with a gun, force exerted by hammer on a nail etc.

4. Frictional Force

Friction is a force that resists the movement of one surface over another. Friction is the property that objects have which makes them resist being moved across one another. If two objects with flat surfaces are placed one on top of the other, the top object can be lifted without any resistance except that of gravity. But if one object is pushed or pulled along the surface of the other, there is a resistance caused by friction. Friction has many important uses. It makes the wheels of a locomotive grip the rails of the track. It allows a conveyor bell to turn on pulleys without slipping. You could not walk without friction to keep your shoes from sliding on the pavement. This is why it is hard to walk on ice. The smooth surface of the ice produces less friction than a pavement and allows shoes to slip.

Friction can be broadly categorized into Static Friction, Kinetic Friction, Sliding Friction, Rolling Friction and Fluid Friction.

1. Static Friction prevents objects from moving when a force is applied to them.

2. Kinetic Friction between two surfaces in contact is the force of friction which comes into play when there is relative motion between the surfaces.

3. Sliding friction is the friction experienced when one object slides over another.

4. Rolling Friction between two surfaces in contact is the force of friction which comes into play when a body rolls over another. This is the principle on which ball bearings work.

5. Fluid Friction occurs when an object moves through a liquid or gas. It is also called as Drag.

Due to the existence of friction we can walk on the ground, trains can run on rails. Frictional force offered by air helps the parachute to have a slow landing. Friction offered by atmospheric air is protecting us from being hit by meteors. A lubricant is a substance which forms a thin layer between two surfaces in contact. Generally oil and grease are used as lubricants to reduce friction as well as to protect the moving parts from overheating. A modern lubricant is a mixture of mineral oil, vegetable oil and colloidal thin oil. Flow of compressed pure dry air acts as lubricant. Graphite is a solid lubricant.

5. Centrifugal Force

Centrifugal force is a force that acts on a body moving in a circular path and is directed away from the centre around which the body is moving. Centrifugal force helps to separate cream from milk.

Example - Suppose a fast-moving bus is making a sudden turn. If there are passengers who are not holding on tightly, they will be thrown in the opposite direction of the turn. This is due to centrifugal force. Centrifugal force is the force that pushes an object moving in a circle away from the center of its path. Roads are built to slope inwards on curves to prevent vehicles from being thrown out due to this force when they turn.

6. Centripetal Force

Centripetal force is a force which acts on a body moving in a circular path and is directed towards the centre around which the body is moving. The centripetal force is the force that causes an object to accelerate in a circle. The direction of the centripetal force and the centripetal acceleration are towards the center of the circle.  Centripetal force is necessary to keep an object moving in a curved path. When a man circles round the earth in a spacecraft, his mass remains constant but weight becomes zero.

7. Magnetic Force

The force between the iron and the magnet is a magnetic force. for instance, the magnetic poles in a DC motor.

8. Gravity Force

Force of attraction between any two bodies in the universe is known as Gravitation. The attractive force of earth, or other celestial body, on an object is called Gravity Force.

9. Cohesion and Adhesion

The force of attraction between like molecules is called Cohesion and the force of attraction between unlike molecules is called Adhesion.

10. Electrostatic Force

Electrostatic force is the attractive or repulsive force between two electrically charged objects.

11. Te​nsion

The force exerted at any point in the wire or string or rope or rod is called the tension at that point.

12. Sprin​g Force 

Springs resists attempts to change their length. This is because of Spring Force. The unit of spring constant is Newton/metre. This equation is also called as Hooke’s law.

Gravitation

Force of attraction between any two bodies in the universe is known as Gravitation. The attractive force of earth, or other celestial body, on an object is called Gravity Force. Because of gravity, the earth and other planets remain in their orbits around the sun; the moon remains in its orbit around the earth; tides are formed; for heating the interiors of new stars and planets to extremely high temperatures; for natural convection, which is the process by which fluid flows under the influence of gravity and a density gradient; and for a number of other earthly phenomena. Gravitational field is the space around a massive body in which gravitational force of attraction is felt. Planets move slower along their orbits when they are farthest from the sun (at apogee) and they move faster along their orbits when they are nearest to the sun (at perigee).

Acceleration due to gravity (g)

The earth attracts every body towards its centre. The acceleration with which the freely falling bodies are attracted towards the earth is called the acceleration due to gravity (g). Normally the value of g is taken as 9.8 m/s². The value of ‘g’ at the centre of earth is zero. The value of ‘g’ is maximum at polar region and minimum at equatorial region. The value of ‘g’ decreases due to rotation of earth. The value of ‘g’ decreases with height or depth from earth’s surface. The acceleration due to gravity is maximum on Jupiter and minimum on planet Mercury.

As the mass of the substances increases the gravitational force between them also increases. The weight of a body on earth is maximum in the polar region and minimum in the equatorial region. In the absence of an effective force of gravity, bodies become weightless in artificial satellites. The weight of a body on the moon will be less than its weight on the earth. This is so because the mass of the moon is 1/81 of the mass of the earth, its radius is 1/3.66 of the radius of the earth. Therefore, the acceleration due to gravity experienced on the moon will be less than the acceleration due to gravity experienced on the earth. This will be about 1/6 of that on earth.

Orbital Velocity

Orbit is the path of a natural or artificial object that moves under the influence of a central force. Orbital velocity is the velocity at which a body revolves around the other body. The orbital velocity of a satellite does not depend on the mass of the body. It depends upon the radius of the orbit. Greater the radius of orbit, lesser will be the orbital velocity. The orbital velocity of a satellite revolving near the surface of earth is 7.9 km/sec.

Period of Revolution

Time taken by a satellite to complete one revolution in its orbit is called its period of revolution. Period of Revolution of a satellite depends upon the height of satellite from the surface of earth. Greater the height, more will be the period of revolution. Period of Revolution of a satellite is independent of its mass.

Geo-Stationary Satellite

A satellite with an orbital period same as the Earth’s rotation period is called geo-stationary satellite. Its period of rotation is 24 hours. Geo-stationary satellite revolves around the earth at a height of 36000 km. The orbit of geo-stationary satellite is called parking orbit.

Escape Velocity

Escape Velocity is the minimum speed which a body must have to escape from the earth’s gravitational force. Escape Velocity of moon is 2.4 km/s and that of earth is 11.2 km/s (7 miles/sec). The escape velocity of the planet Jupiter is 60 km/s and of Mercury it is 4.2 km/s.

Kepler's laws of planetary motion

Three laws discovered by the German astronomer Johannes Kepler regarding the motion of planets in the solar system.

1. First Law (Law of Orbits)

All planets move in elliptical orbits around the Sun, which is located at one of its foci. This law is a major change from the Copernicus model, which prescribed only circular paths for planetary motion.

2. Second Law (Law of Areas)

A straight line connecting a planet and the Sun moves at equal intervals of time. Planets move more slowly when they are farther from the Sun and faster when they are closer.

3. Third Law (Law of Periods)

The square of the period of a planet's orbit is proportional to the cube of the semi-major axis of its elliptical orbit.

Newton’s Law of Universal Gravitation

Every particle in the universe attracts every other particles with a force which is directly proportional to the product of their masses and inversely proportional to the square of distance between them.

F = G.Mm/r²

Where ‘G’ is gravitational constant and value of ‘G’ is 6.67 x 10^-11 Nm²/kg²

Viscosity

Viscosity refers to the internal frictional forces in a fluid that resist flow. In liquids it is due to intermolecular cohesive forces, while in gases it is due to the movement of molecules in different regions of the gas running at different speeds. Around 1600, the English physicist Sir Issac Newton formulated more appropriate ideas. Those substances requiring a certain amount of force to be applied before flow occurs are said to have plastic flow. Further developments of Newton's ideas came from the French physician Jean Poiseuille in 1844 and from Sir George Stokes (England) in 1850, the latter showing that objects falling through a viscous liquid reach a steady velocity known as the terminal velocity.

The viscous force is the force that opposes relative motion between layers of liquid or gas. Viscosity is the characteristic of a liquid that causes forces to be applied between layers to lessen their relative motion. The liquid flows in different layers. The topmost layer will be moving as quickly as possible. The velocities of the lower layers will be lower. The frictional force between liquid layers (also known as the viscous force) is the cause of this variation in velocity from layer to layer. Different liquids have varying viscosities. A liquid's viscosity reduces as its temperature rises. Compared to liquids, gases have a substantially lower viscosity. Diffusion of a gas's molecules from one layer causes its viscosity. There is no viscosity in solids. Liquid and gases are together called fluid. Viscosity of an ideal fluid is zero.  

Viscous Liquids and Mobile Liquids

Liquids of large viscosity are called viscous liquids. Examples of viscous liquids are Glycerine, Honey, Castor Oil etc. Liquids of small viscosity are called mobile liquids. They can easily flow. Examples of mobile liquids are Water, Kerosene etc.

SI unit of viscosity - Poiseuille (PI)

Other units - Nsm^-2 or Pa S

Dimension of viscosity - [ML^-1T^-1]

Viscosity Questions and Answers

1. Define the coefficient of viscosity.

Ans: It is the tangential force necessary to keep a unit velocity gradient amid two layers each of unit area. 

2. Define fluid.

Ans: Fluid is a substance which begins to flow when external force is applied on it.

3. Give example for fluids?

Ans: Liquids and gases.

4. Define viscosity.

Ans: Viscosity is a fluid property in which an internal frictional force acts while the fluid is in motion and resist the relative motion. 

5. What is Stoke's formula?

Ans: F=6πrηv , Where r = radius, η = fluid velocity, v = sphere velocity

6. What is meant by Reynold's number?

Ans: Rn=(ρVL)/μ , Where ρ = density, V = flow speed, L = linear dimension, μ = dynamic velocity

7. Give the Newton's equation for viscous force.

Ans: F= -ηA(dvx/dz)

8. Define the unit 'poise'

Ans: It is the unit of viscosity in C.G.S system. The unit is in honor of Poiseuille who did important works on viscosity

1 poise = 1 dyne second/cm²

9. What is meant by terminal velocity?

Ans: Terminal Velocity is defined as the maximum constant velocity attained by a body when falling freely in a viscous medium.

10. What happens to viscosity of a liquid when temperature increases?

Ans: Viscosity decreases

11. What happens to viscosity of a liquid when pressure increases?

Ans: Viscosity increases (except water) 

12. What is the effect of temperature on viscosity of liquids?

Ans: Viscosity decrease with the increase in temperature.

13. What is the effect of temperature on the viscosity of gases?

Ans: The viscosity of gasses increase with rise in temperature.

Surface Tension

A liquid's surface tension causes its free surface to behave like an elastic membrane that has been stretched, giving it a tendency to contract. Surface Tension is caused by unbalanced molecular cohensive force. The surface tension decreases with rise of temperature. There is more energy on a larger surface. Most fluids take on the shape with the least surface area in order to minimize energy. For a given volume, the sphere has the minimum surface area. Hence it assumes spherical shape. Hence rain drops and mist drops are spherical in shape. When the shaving brush is removed from water, hair of the brush cling together due to surface tension.

A liquid of large surface tension cannot wet a surface easily. A surface is readily wetted by a liquid with a lower surface tension. Water wets surfaces because it has a low surface tension. When soap is added to water, the surface tension of water decreases. Therefore soap water can wet a surface more easily than pure water. The soap water having less surface tension, can enter into the tiny pores of the clothes and remove the dirt. This is why soap water is preffered for cleaning purposes. When temperature increases, the surface tension of water decreases, so hot water is preferred for cleaning purposes.

Examples related to the surface tension of liquids

1. Oil and water do not mix.

2. Ducks swimming in water do not get wet.

3. Water and salts reach the leaves of trees at high altitudes.

4. The fibers of a paintbrush do not mix when they are dry or submerged in water. But when they are taken out of the water, they mix and become a sharp point.

Capillarity

Surface Tension is responsible for the phenomenon called Capillarity. Capillarity is the ability of the liquid to defy gravity and travel up through tiny pores. Capillarity is responsible for the rise of water in plants and the wick of a lamp taking up oil. Farmers loosen the soil and break it up into fragments to stop water loss from capillary action. Capillarity is due to adhesive force. Capillarity is also the tendency of liquids to move into hair like passageways. These hair like passageways called capillaries which occur as fine pores in solid materials. A paper towel, for example, contains millions of capillaries between in fibres. The passageways absorb water by capillarity. The narrower the capillary, the greater is its ability to absorb or repel a liquid. Capillarity has many benefits. It draws water through soil to the roots of plants. 

Surface Tension Questions and Answers

1. Define surface tension

Ans: It is defined as the force acting tangential to the liquid surface and perpendicular to unit length of an imaginary line drawn on the surface of the liquid

2. What is the unit and dimension of Surface Tension?

Ans: Unit - Nm^-1; Dimension - MLT^-1

3. How is surface tension related to surface energy?

Ans: They are the same.

4. What is the difference between adhesive and cohesive forces?

Ans: Attraction between molecules of the same kind-cohesive. Attraction between molecules of different kind-adhesive.

5. What is angle of contact?

Ans: The angle between the tangent to the liquid surface at the point of contact and the solid inside the liquid.

6. What is meant by capillarity?

Ans: Rise of liquid in capillary tube is called capillarity

7. For mercury there is capillary depression. Why?

Ans: Angle of contact is oblige (140°)

8. What are the factors on which capillary ascent depends?

Ans: Inversely proportion to the radius, inversely proportional to density and directly proportional to surface tension.

9. If the angle of contact were 90°. What is capillary accent?

Ans: Zero

10. Is surface tension is a molecular phenomenon or atomic

Ans: Molecular phenomena.

11. What is a capillary?

Ans: A tube with fine bore.

12. What is the unit of surface tension?

Ans: N/m

13. Give the value of surface tension of water?

Ans: It is 72.7 x  10^-3 N/m at 20° C

14. Define capillary rise.

Ans: Rising of a liquid in a capillary tube is called capillary rise.

15. Why doesn't mercury rise in the capillary tube?

Ans: For mercury and clean glass, the angle of contact is obtuse. Hence mercury does not rise in the capillary tube.

16. Why does water rise in the capillary tube?

Ans: For water and clean glass, the angle of contact is acute. Hence water rises in the capillary tube.

17. How does surface tension vary with temperature?

Ans: Surface tension decreases with increase in temperature.

Elasticity and Plasticity

Elasticity 

Elastic force is the internal force that an object exerts on an object when a force is applied to it. Elastic force always tries to return objects to its initial size and shape. Materials differ in their degree of elasticity. The first person to make a scientific study of it was the English physicist Robert Hooke in 1678. A spring is a device that stores force. Springs are used to reduce sudden shocks in many machines, devices, and vehicle parts. When an attempt is made to pull a spring coil, elasticity is the tendency of the spring to return to its original position. Rubber, glass, and steel are other materials that exhibit elasticity. Glass is more elastic than steel and steel is more elastic than rubber. Elasticity is manifested in materials that are compressed or stretched.

Plasticity 

A body is said to be plastic if, upon removal of the deforming force, it does not return to its initial size and shape; this characteristic is known as plasticity.

Example - Clay, Plasticine etc.

Elastic Limit 

It is the maximum value of deforming force upto which a material shows elastic property and above which the material looses its elastic property.

Hooke's Law

According to Hooke's Law, a body's length changes in proportion to the force applied up to the material's elastic limit.

Stress and Strain

The principle of Hooke's law states that the stress applied to a solid object and the resulting deformation (strain) of the object are proportional within the elastic limit. Stress is the internal force per unit area of cross section of a strained body. 

i.e, Stress = Force/Area

The SI unit of Stress is Nm^-2 or Pascal

C.G.S unit of Stress is dyne cm^-2

1 Giga Pascal (1GPa) = 10⁹ Pa

The ratio of change in dimension to the original dimension is called strain. It has no unit.

Heat and Temperature

Temperature is the degree of hotness and heat is a form of energy which increases the temperature of a body. 

Heat - Heat is the unit of total kinetic energy of molecules in a Particle. A scientific explanation of heat escaped scientists for many years. At first interest centered on the construction of thermometers. By 1760, the scottish chemist, Joseph Black had proved the difference between temperature and heat. Two theories of heat arose; one stated that heat was a fluid named caloric, capable of moving from one object to another. The other theory was that heat was a kind of vibration. In 1798, the English physicist Count Rumford noticed the heat created by boring a cannon and decided that heat was caused by friction. Other researchers in this field were Sir Humphry Davy (England) in 1799 and Frenchmen, Jean Fourier in 1822 and Nicolas Carnot in 1824. James Joule (England) showed in 1847 that heat was a form of Energy.

Temperature - Temperature is the unit of average kinetic energy of molecules in an object. Temperature is how hot or cold something is as measured on a particular scale. The concept of temperature is closely related to the flow of heat between two connected objects of different temperatures. Heat always flows from the hotter object to the cooler one. Instruments that measure temperature are called Thermometers. A scale marked on the thermometer indicates each level of hotness. The two most common temperature scales used on thermometers are celsius and fahrenheit. Temperatures on all scales are based on the International Temperature Scale of 1990. Scientists often speak of thermodynamic temperature, a fundamental physical quality completely independent of the properties of a substance. The SI unit of thermodynamic temperature is the Kelvin, indicated by K. Normally the temperature was measured in Celcius Scale. Commonly used temperature scales are Celsius scale, Fahrenheit scale and Kelvin scale. Pyrometer is the instrument used to measure high temperatures and Cryometer is the instrument used to measure low temperatures. 

Cryogenics - Cryogenics is the study of extremely low temperatures. It is concerned with the production, control and application of extremely low temperatures. It includes the development of techniques that produce and maintain such temperature for industrial and scientific use. Temperatures of primary interest in cryogenics range from about -120°C to almost absolute zero -273.15°C. Absolute zero is, theoretically, the lowest temperature a gas can reach. Absolute Zero is the temperature at which the kinetic energy of molecules becomes zero and is also the temperature at which all the molecules in a substance completely stop moving. 

Note - At ultra high temperature matter exist in plasma form. 99% of matter in the Universe is in plasma form.

Thermometer 

The measurement of temperature could be said to have started with the invention of the thermometer by Galileo in Italy in 1593. Thermometer is an instrument that measures the temperature of gases, liquids and solids. Mercury Thermometer was discovered by Farenheit. Mercury is the liquid used in Thermometers. Mercury is found in the bulb at the tip of the thermometer. The action of a thermometer is based on the fact that certain measurable physical characteristics of substances change when the temperature changes. These characteristics include the volume of a liquid and the length of a solid. Another is the resistance - that is, the opposition to the flow of electricity - in an electrical conductor. There are three principal types of thermometers. (1) liquid-in-glass, (2) deformation type and (3) electrical. Many types of thermometers are made as both digital thermometers and disposable thermometers. 

Various Types of Thermometers - Laboratory thermometers and clinical thermometers are the two types of thermometers work by utilizing the ability of liquids to contract and expand. The clinical thermometer is specially designed to measure human body temperature. Normal human body temperature is 36.9°C (or 98.4°F). Sir.Thomas Albert invented clinical thermometer. Farenheit is the scale used in clinical thermometer. Laboratory thermometers are used to measure the temperature below 200°C.

Heat Energy - Joule is the unit of Heat Energy. Heat Energy is also measured in Calorie unit. One calorie is the amount of heat needed to raise the temperature of 1 gm of water by 1°C. One calorie is equal to 4.2 Joule. 

• Heat required to melt 1 kg of ice at 0°C - 3.33 × 10⁵ J

• Heat required to vaporize 1 kg of water at 100°C - 22.6 × 10⁵ J

Thermal Expansion

The increase in the size of an object due to an increase in temperature is known as Thermal Expansion. Gases expand the most when heated and solids expand the least when heated. 

Examples of Thermal Expansion

1. When a thermometer is placed in hot water, the mercury in it rises

2. When a partially inflated balloon is placed in a warm room, it expands and becomes larger

Various cases where thermal expansion of objects has been considered

• Gaps are made between railway tracks.

• Iron straps are put on the wheels of a bullock cart.

• Gaps are made between concrete buildings.

• Gaps are made in concrete bridges.

Types of Thermal Expansion

1. Linear Expansion - The expansion along the length of an object due to an increase in temperature is known as Linear Expansion.

2. Area Expansion - The expansion along the surface of an object due to an increase in temperature is known as Area Expansion.

3. Volume Expansion - The expansion that occurs within an object as a result of an increase in temperature is known as Volume Expansion.

Transmission of Heat

The transfer of heat from one place to other place is called transmission of heat. There are three modes of heat transfer - Conduction, Convection and Radiation.

1. Conduction

Conduction is the process by which heat is transferred as a result of a temperature difference between two adjacent parts of an object. Here heat is transferred from one place to other place by the successive vibrations of the particles of the medium without bodily movement of the particles of the medium. In solids, heat transfer takes place by conduction. Gases are relatively poor conductors of heat. However, the conductivity of liquids is between that of solids and gases.

2. Convection

Convection is the process of heat transfer by the actual movement of particles from one place to other place. It is possible only in fluids. It is the process by which heat is transferred in liquids and gases. Convection is possible due to the overall movement of various parts of the fluid. Forced Convection and Natural Convection are the two types of Convection.

i. Forced Convection - Forced Convection is a process of convection that is possible due to the influence of a pump or some other physical conditions. Examples of Forced Convection are

• Forced Air heating systems in home

• Circulatory system in humans

• Cooling system in automobile engines

ii. Natural Convection

Examples of Natural Convection

• Sea breezes and land breezes

• Trade winds

3. Radiation

Radiation is a method of heat transfer from one point to another without heating the medium. Here, heat energy is transmitted through electromagnetic waves. The energy radiated by electromagnetic waves is called radiant energy. This is the process by which heat from the sun reaches the earth. A person standing under a bulb gets heat due to radiation.

Conductors and Insulators of Heat

Ebonite and Asbestos are the worst conductor of heat. Example of good conductors are silver, copper, mercury etc. Very poor conductor, such as glass are called Insulators. Air is a good insulator. Mica is a good conductor of heat, but a bad conductor of electricity. Air is one of the worst conductor, this keeps house warmer in winter and cooler in summer. Black surface is a good radiator as well as good absorber of heat. White clothes are preffered in summer, as these absorb less heat from the surroundings. Perspiration is maximum, when temperature is high and air is humid. Evaporation takes place at all temperatures and is accompanied by cooling.

Anomalous Expansion of Water

Almost every liquid expands with the increase in temperature. But when temperature of water is increased from 0°C to 4°C its volume decreases. If the temperature is increased above 4°C the volume starts increasing.

Superfluidity and Superconductivity

Superfluidity is the phenomenon in which the viscosity of some liquids completely disappears at very high temperatures. Superconductivity is the phenomenon in which the electrical resistance of some materials completely disappears when the temperature is lowered to a certain temperature. Superconductivity was discovered by Kamerlingh Onnes (1911). The temperature at which mercury exhibits superconductivity is 4.2 Kelvin.

Specific Heat Capacity

Heat Capacity of a substance is the amount of heat needed to raise the temperature of the substance through 1°C. Specific Heat Capacity is the amount of heat needed to raise the temperature of a substance of one kilogram mass by 1 K. Specific Heat Capacity depends on the nature of the substance and its temperature. The unit of Specific Heat Capacity is joule/kilogram Kelvin (J/KgK). The substance with the highest Specific Heat Capacity is water and the element with the highest Specific Heat Capacity is Hydrogen. The substance with the lowest Specific Heat Capacity is gold.

Substances and their specific heats

• Aluminum - 900.0 J/KgK

• Ice - 2060 J/KgK

• Carbon - 506.5 J/KgK

• Glass - 840 J/KgK

• Copper - 386.4 J/KgK

• Iron - 450 J/KgK

• Lead - 127.7 J/KgK

• Kerosene - 2118 J/KgK

• Silver - 236.1 J/KgK

• Edible oil - 1965 J/KgK

• Tungsten - 134.4 J/KgK

• Mercury - 140 J/KgK

Specific Heat Capacity of Water is useful in:

• The change in ambient temperature does not immediately affect our body.

• Water is used as a coolant in radiators in engines.

• The Specific Heat Capacity of sand is 1/5 of the Specific Heat Capacity of water.

• Land heats up and cools down 5 times faster than water.

• The Specific Heat Capacity of water is 4200 JKg^-1K^-1

Principle of Mixture

When two objects of different temperatures are in contact, heat will flow from the object with higher temperature to the object with lower temperature until the temperatures of both become equal. The heat loss of the hot object is equal to the heat gain of the cold object. This is the principle of mixture.

Change of State

The transition from one of the common states of matter, solid, liquid, or gas, to another is called a change of state. A change of state is a physical change that occurs in a substance as a result of the absorption or release of heat. To change the substance from one state to other state, the substance is either heated or heat is removed from the substance. Change of state takes place at a fixed temperature. Melting, Freezing or Fusion and Vapourisation is the three change of states.

1. Melting - The change of state in which a solid changes to a liquid is called melting.

2. Fusion (Freezing) - The change of state in which a liquid changes to a solid is called fusion.

3. Vapourisation - The process by which a substance is changed from liquid state to vapour state is called Vapourisation. Vapourisation takes place by Evaporation and Boiling.

Evaporation - Evaporation is the process of vapourisation which takes place only from the exposed surface of liquid and that at all temperatures. Evaporation causes cooling. Evaporation is the working principle of Refrigerator. 

Examples of how evaporation is used in everyday life:

• Water stored in a clay pot cools down well

• A sweating person feels cooler when sitting under a fan.

• A person feels cold when waving a wet hand.

4. Sublimation - Not all substances go through the three states of solid - liquid - gas. Some substances go directly from the solid state to the gas state. The process of changing state directly from the solid state to the gas state is called sublimation. Dry ice (solid CO₂), iodine, and camphor are examples of sublimation. During sublimation, the solid and gas states of a substance are in thermal equilibrium. Sublimation takes place when boiling point is less than melting point.

5. Condensation - It is the process by which a substance is changed from vapour state to liquid state.

Phase Change Point

A phase change is the process by which the physical properties of a substance like solid, liquid or gas changes. A phase change point (phase transition point) is the point at which a substance changes phase.

1. Melting Point - When a substance changes from a solid to a liquid, the solid and liquid states exist together in thermal equilibrium. The temperature at which thermal equilibrium exists is called the melting point. Simply, it is the temperature at which a substance changes from a solid to a liquid. The melting points of different substances vary considerably. For example, tungsten has an extremely high melting point, 3410°C, but solid hydrogen melts at the low temperature of -259°C. The melting point of a material depends partly on whether the material is a pure substance or a mixture. A pure substance is either a pure element, such as iron or a simple compound, such as water. A mixture consists of two or more substances that are not chemically combined. The melting point of a substance at a standard atmospheric pressure is called the normal melting point. 

2. Boiling Point - Boiling is the process of vapourisation which takes place at a fixed temperature and from whole part of liquid. The temperature at which the liquid and gaseous states of a substance exist together is called the boiling point. Boiling point is the temperature at which a liquid boils and turns into a vapor at normal atmospheric pressure.  Boiling point of a liquid increases with the increase in pressure.

3. Freezing Point - The temperature at which a liquid changes to a solid at normal pressure. 

Various Temperatures

• Lowest temperature at which absolute zero can be reached : -273°C

• Temperature at which water experiences maximum density : 4°C

• Temperature at which water experiences minimum volume : 4°C

• Temperature at which mercury becomes solid : -39°C

• Human body temperature : 36.9°C/98.4°F/310 K

• Boiling point of water in a pressure cooker : 120°C

• Temperature used in the manufacture of ammonia : 500°C

• Temperature at the surface of the Sun : 5500°C

• Melting point of gold : 1063°C

• Melting point of tungsten : 3410°C

• Melting point of alcohol : -115°C

• Melting point of mercury : -39°C

• Melting point of water : 0°C (32° F, 273 K)

• Boiling point of water : 100°C (212°F, 373 K)

Latent Heat

The amount of heat required to change the state of unit mass of substance at constant temperature is called Latent Heat. It comes in two main types.

1. Latent Heat of Fusion

The latent heat of fusion is the amount of heat required to completely convert one kilogram of a solid to a liquid at its melting point without changing its temperature. The unit of latent heat of fusion is joule/kilogram (J/kg). For 1Kg of ice it is 334000 J/kg.

2. Latent Heat of Evaporation

The latent heat of vaporisation is the amount of heat required to completely convert one kilogram of a liquid to a gas at its boiling point without changing its temperature. Steam burns are more deadly than burns from boiling water because of the higher latent heat of vapourisation. For water the latent heat of vapourisation is 22,60,000 J/kg. This is why burn from steam may be more serious than the boiling water.

Substance	Melting point (°C)	Latent heat of fusion (105J/kg)	Boiling point (°C)	Latent heat of vaporization (105J/kg)
Ethanol	-114	1.0	78	8.5
Gold	1063	0.645	2660	15.8
Lead	328	0.25	1744	8.67
Mercury	-39	0.12	357	2.7
Nitrogen	-210	0.26	-196	2.0
Oxygen	-219	0.14	-183	2.1
Water	0	3.33	100	22.6

Note:

• Heat Engine is a device which changes heat energy obtained by burning a fuel to kinetic energy. For example, Internal combustion engine used in vehicles. Steam Turbines are used in power stations and on ships.

• Water pipes breaks in winter in cold regions. This is because water expands on freezing. Due to this reason when water is filled in a bottle and is allowed to freeze the bottle breaks.

• A freezing mixture is a mixture of ice and salt.

• The phenomenon that helps to skate through ice is called regelation.

Temperature Scales and their Interconversion

The measurement of temperature could be said to have started with the invention of the thermometer by Galileo in Italy in 1593. However, there was no general agreement on a standard set of measurements until temperature scales were devised. The German physicist Gabriel Fahrenheit created a scale in 1714 that determined the boiling and freezing points of water to be 212 and 32, respectively. In 1742, the Swedish astronomer Anders Celsius devised another scale called Celsius Scale. He set the freezing point for water at zero and the boiling point at 100. Because of its 100 degree marks, the Celsius scale became known as the centigrade scale. In 1948, scientists at an international conference renamed it the Celsius scale. It is favored by scientists over the Fahrenheit scale for several reasons, one being its use of 100 degrees between key marks rather than 180. Commonly used temperature scales are Celsius scale, Fahrenheit scale, Kelvin scale or Absolute scale and Reaumur scale.

1. Celsius Scale

Celsius Scale is a scale for measuring temperature. It is a part of the metric system of measurement. People in all major countries use the Celsius scale for everyday temperature measurement. Scientists throughout the world also use this temperature scale. On the Celsius scale, 0° is the freezing point of water and 100° is the boiling point. The Celsius scale is sometimes called the centigrade scale, because the word means 'divided into 100 parts'. The body temperature in Celsius scale is 37° and room temperature is 20°. The Celsius scale was originally developed in 1742 by the Swedish astronomer Anders Celsius. It was later changed and improved. The ninth general conference of weights and measures officially named the Scale, the Celsius Scale in 1948.

2. Kelvin Scale or Absolute Scale

The law of gases discovered in 1787 by the French physicist Jacques Charles was puzzling to the Scottish scientist, Lord Kelvin. In 1848, Kelvin realized that at -273 degrees centigrade the energy of the gas molecules would be zero. He theorized that this would hold for any substance and that this temperature represented the lowest temperature possible or absolute zero. He devised a new temperature scale with degrees the same size as those of the centigrade plus 273. The letter K is used to identify the scale called 'degrees kelvin'. In absolute or kelvin scale, the upper fixed point is 373.15 K and the lower fixed point is 273.15 K. Absolute Zero is the lowest possible temperature which is equal to 0K or -273.15°C or -459.67°F. In Kelvin Scale, there is no negative temperature. In Kelvin Scale, -273°C is equal to 0K and 0°C is equal to 273K. Also 100°C is equal to 373K.

3. Fahrenheit Scale

The first exact measurements of temperature were in Fahrenheit. In 1714, Dutch physicist, Gabriel.D.Fahrenheit, invented a mercury-based thermometer. The Royal Society of England claims that this was the first accurate and useful thermometer ever made. In a Fahrenheit scale, the unit is expressed as a number followed by °F, or simply F. On this scale, water has a freezing point of 32 and a boiling point of 212.

4. Reaumur scale

The Reaumur scale, also referred to as the "octogesimal division," is a temperature scale that defines the melting and boiling temperatures of water as 0 and 80. The Physicist, Reaumur developed this scale in 1730 and this scale is named after him.

The Relationship between the Four Temperature Scales

C/5 = (F - 32)/9 = (K - 273)/5 = R/4

where, C - Temperature in Celsius Scale; F - Temperature in Fahrenheit Scale; K - Temperature in Kelvin Scale; R - Temperature in Reaumur Scale

Interconversions

a. Conversion of Fahrenheit Scale to Celsius Scale, C = (F - 32) x 5/9

b. Conversion of Celsius Scale to Fahrenheit Scale, F = (C x 9/5) + 32

c. Conversion of Celsius Scale to Kelvin Scale, K = C + 273.15

d. Conversion of Kelvin Scale to Celsius Scale, C = K - 273.15

e. Conversion of Fahrenheit Scale to Kelvin Scale, K = 5/9 (F − 32) + 273.15

f. Conversion of Kelvin Scale to Fahrenheit Scale, F = 9/5 (K − 273.15) + 32

Instant Converter

a. 0°C = 32°F = 273K

b. 100°C = 212°F = 373K

c. -40°C = -40°F (here the values will be same for both celsius and farenheit scale)

d. 574.25K = 574.25°F (here the values will be same for both kelvin and farenheit scale)

Note : There is no same value in conversions of both celsius and kelvin scale.

Thermodynamics

The study of different types of energy, including heat and work, as well the conversion of energy from one form into another, is known as thermodynamics. Engineers, chemists and physicists use the principles of thermodynamics in understanding events in nature and in such activities as designing machines and calculating the loss or gain of energy in chemical reactions. Thermodynamics is based chiefly on three laws.

First Law of Thermodynamics

According to the first law, energy cannot be created or destroyed in a system, which could be anything from a simple object to a complex machine. Rather, energy is converted from one form into another or transferred from one system to another. First law of thermodynamics is also called as the law of conservation of energy. Mathematically, it may be expressed as 

ΔQ = ΔU + W

Where,

ΔQ is the heat given or lost;

ΔU is the change in internal energy;

W is the work done;

Second Law of Thermodynamics

The second law of thermodynamics deals with the natural direction of energy processes. This law states that heat can only flow from a hotter object to a colder object. The law simply states that the entropy of an isolated system will never diminish over time. Mathematically, it may be expressed as

ΔS = ΔQ/T

Where,

ΔS is the Entropy;

ΔQ is the heat given or lost;

T is the Temperature;

Third Law of Thermodynamics

The third law of thermodynamics states that the entropy of a system approaches a constant value when the temperature approaches Zero Kelvin (absolute zero). At absolute zero temperature, the entropy of a perfect crystal is zero. Mathematically, it may be expressed as

S – S₀ = 𝑘_B ln𝛀

Where,

S = Entropy of the system;

S₀ = Initial entropy;

𝑘_B - Boltzmann constant;

𝛀 - total number of microstates that are consistent with the system’s macroscopic configuration;

For a perfect crystal, 𝛀 = 1, therefore, the above equation can be written as

S – S₀ = 𝑘_B ln(1) = 0 (since ln(1) = 0)

If the initial entropy (S₀) of the system is zero, the following value of ‘S’ can be obtained:

S – 0 = 0

⇒ S = 0

Thus, the entropy of a perfect crystal at absolute zero temperature is zero.

Humidity and Relative Humidity

Humidity is the amount of water vapour in the air. Relative Humidity is the percentage of water vapour that the air can hold at a given temperature. A hygrometer is an instrument that measures relative humidity. Relative humidity increases as the temperature of the air increases. The maximum value of relative humidity is 1.

Absolute Humidity is the actual amount of water vapour in the air. Absolute humidity is measured in grams of water vapour per cubic meter of air (g/m³). If the relative humidity is half of the water vapour that the atmosphere can hold at a given temperature, then the absolute humidity is 50%. Relative humidity is 100 percent at saturation.

Relative Humidity = (Absolute humidity / Total water vapour that the atmosphere can hold) x 100

Saturation Level refers to the maximum amount of water vapour that the air can hold at a given temperature. Condensation begins when the air is saturated with water vapour. The critical temperature at which condensation begins is known as Dew Point.

Wet and Dry Bulb Thermometer

A wet and dry bulb thermometer is an instrument used to measure relative humidity. The number of thermometers in a wet and dry bulb thermometer is two. One thermometer in the wet and dry bulb records the normal ambient temperature. The other thermometer in the wet and dry bulb records a temperature lower than the normal temperature. Relative humidity is calculated based on the difference in temperature between two thermometers. When the temperature difference is greater, the relative humidity will be lower. When the temperature difference is smaller, the relative humidity will be higher.

Temperature - Humidity Index

Temperature - Humidity Index also called THI, is a scale of values that serves as an estimate to predict how comfortable people will feel in hot weather. The values of the scale depend on air temperature and relative humidity that is, the actual moisture in the air compared with the most moisture the air could hold. They do not include the effects of wind and sunshine. However, the scale does help indicate how some people may be affected when high temperature and humidity are combined. The higher a temperature-humidity index reading is, the more uncomfortable people are. Most people will feel comfortable with a temperature humidity index below 75. Half or more will feel uncomfortable when the index is between 75 and 80. When the index reaches 80, most people will be uncomfortable. Serious health hazards, such as tiredness, dizziness, heat stroke and heat exhaustion, can occur when the index reaches 85 or more.

Density and Relative Density

Density - Density is the mass of a substance per unit volume. Substances are densest in the solid state and least dense in the gaseous state. Liquids are largely incompressible, so their density is approximately constant at all pressures. Gases exhibit large variations in density with pressure. Density is a positive non-linear quantity. The density of water is maximum at 4°C and the volume of water is maximum at 0°C. Mercury is the liquid having maximum density (13.6g/cm³).

The density of air decreases with increasing altitude. Substances are densest in the solid state and least dense in the gaseous state. Liquids are generally incompressible to a large extent, so their density is approximately constant at all pressures. Gases exhibit a large change in density with pressure.

The density of a liquid with mass 'm' and 'v' (ρ) = mass/volume = m/v

Examples

• An iron nail floats on mercury but sinks in water because the specific density of iron is lower than that of mercury and higher than that of water.

• A petrol fire cannot be extinguished by throwing water on it since the density of water is more than the density of petrol, water sinks below the petrol when it is poured over a petrol fire.

• The density of sea water is higher than the density of river water, therefore it is easier to swim in the sea than in river. This is why a ship entering from river mouth to sea rises up a little.

• Ice floats on water because its weight is less than the weight of an equal volume of water.

• Ice floats on water but sinks in alcohol because the density of alcohol is lower than that of water.

Unit and Dimension of Density

• Unit of density = g/cm³ or kg/m³

• Dimension of density - [ML^-3]

• SI unit - kg/m³

Various Densities

• Density of water - 1000 kg/m³

• Density of sea water - 1027 kg/m³

• Density of crude oil - 810 kg/m³

Relative Density

The ratio between the density of the substance and the density of water is known as relative density. The density of a substance is calculated by how many times the density of water it is. The density of that substance is calculated based on what that substance is. This statement is called relative density. Since relative density is a ratio, it has no unit. A hydrometer is an instrument used to measure the relative density of liquids. The indication of the hydrometer when placed in water is 1. If a hydrometer is placed in a liquid that is denser than water, the liquid surface will be below the marking 1. In liquids that are denser than water, the hydrometer will not sink further. But in liquids that are less dense than water, the hydrometer will sink further. A lactometer is a device used to measure the water level (relative density) in milk.

Relative density = Density of the substance/Density of water

Floatation and Buoyancy

Floatation 

The law of flotation states that a floating object displaces its own weight of the fluid in which it floats. Law of floatation is an application of Archimedes' principle. 

According to law of flotation, Weight of floating object = Weight of fluid displaced

Archimedes' Principle

Archimedes' principle states that when an object is partially or completely immersed in a liquid, the buoyant force exerted on it is equal to the weight of the liquid it displaces. 

Buoyancy (Buoyant Force)

When a body is immersed partly or wholly in a liquid, a force will acts on the body by the liquid in the upward direction. This force is termed as Buoyant force and is also called as upthrust. Buoyant force is the force that helps an object float in water. Some objects float in liquids due to buoyancy. The buoyancy of an object is the weightlessness that an object feels in the water. The density of the liquid and the volume of the object are factors that affect the buoyancy of an object in the liquid. There are two forces that an object experiences when it is immersed in a liquid - the weight of the object which acts downward, and the buoyancy force which acts upward on the object. The buoyancy of an object when it is immersed in a liquid is calculated by finding the weightlessness of the object in the liquid.

Examples

• Buoyancy is the reason why a hydrogen-filled balloon fly in the air.

• Buoyancy is the reason why a stone feels weightless in water.

• The reason why a ship floats in water is because of buoyancy. 

• If kerosene and water are taken in the same container, the kerosene floats on top of the water because kerosene is less dense than water. 

• Iron sinks in water. But the reason why a ship made of iron floats in water is because the ship can displace more water than the total volume of iron used to build the ship.

Buoyancy Principle

When an object floats in a liquid, the weight of the object is equal to the weight of the liquid it displaces. Also when an object is immersed in a liquid, the volume of the liquid it displaces is equal to the volume of the object. Lactometers and hydrometers are instruments that work on the principle of buoyancy. The lactometer is the device used to test the milk purity based on the principle that greater the density of a liquid, the lesser will be the immersion of an object. 

Pressure, Thrust, Pascal's law

There is an invisible force that always exerts force around us. It is none other than air! This force exerted by air is called atmospheric pressure. It is the pressure exerted on earth surface by the atmosphere. All substances in all states, solid, liquid, and gas, have pressure. The pressure of liquids increases with depth. Swimmers who go underwater sometimes get earaches. This is because the pressure of the surrounding water increases. Atmospheric pressure decreases with altitude. This is because the number of gas molecules in the atmosphere decreases as altitude increases. That is why it is difficult to cook on the mountain and the fountain pen of a passenger leaks on aeroplane at height. Torricelli was the first to measure atmospheric pressure. 

Definition of Pressure

Pressure is defined as force per unit area. In physics, the term is usually applied to fluids. If a fluid is exposed to suitable forces, pressure is produced in it. The greater the force, the greater the pressure. Pressure is measured in kgms per square centimetre or pascals in the metric system. It is measured in pounds per square inch in the imperial system. Atmospheric pressure is one of the most common examples of pressure. It is produced by the weight of the air from the top of the atmosphere as it presses down upon the layers of air below it. At sea level, the average atmospheric pressure is 101.3 kilo pascals. This decreases with altitude because of less air pressing from above. If a fluid is at rest, pressure is transmitted equally to all its parts and at any one point, is the same in all directions. The fluid acts this way because the molecules in it move freely. The molecules are far apart in a gas and comparatively close together in a liquid. 

Thrust and Pressure

The total normal force exerted by a fluid on a surface is called thrust. Its unit is newton (N). The pressure at a point on a surface is the thrust acting normally per unit area around that point.

That is, Pressure = Thrust/Area

The SI unit of Pressure is Newtons per Square Metre (Pascal)

It is possible to liquefy all gases at atmospheric pressure, but it is impossible to liquefy all gases at atmospheric temperature. Gases can be liquefied if subjected to low temperatures or high pressures, but below the critical temperature. The same volume of a gas at constant temperature enclosed in a vessel of small volume will cause greater pressure. Volume of a gas varies inversely with the applied pressure. Doubling the pressure reduces the volume to about half. Increasing the temperature of a gas in a closed container will increase the pressure of the gas.

Various Units of Pressure

• 1 atmosphere = 760 mm of Hg

• 1 Bar = 1 x 10⁵ Nm^-2

• 1 Bar = 0.98692 atmosphere

• 1 Torr = 1/760 of an atmosphere = 1 mm Hg

Liquid Pressure

Liquid pressure is the force exerted by a liquid on a unit volume of water. The molecules of liquid exert a force on all sides of the container in which they are located. Liquid pressure is proportional to the weight of the liquid in the unit volume. In a static liquid at same horizontal level, pressure is same at all points. Pressure at a point in a liquid is proportional to the density of the liquid. The pressure exerted by the liquid increases as the height of the liquid increases. The liquid pressure is the product of the height of the liquid (h), the density of the liquid (d), and the acceleration due to gravity (g).

P = hdg

The boiling point of a liquid increases with increasing pressure and decreases with decreasing pressure. The boiling point of liquids increases when the pressure increases, which is why food can be cooked quickly in a pressure cooker. The average temperature at which water boils in a pressure cooker is 120°C. When the pressure increases, the melting point of ice decreases, resulting in the melting of ice. When the pressure decreases, the melted ice condenses. This phenomenon is called refreezing. Manometer is a device used to measure pressure exerted by liquids. 

Pascal's law

Pascal's law states that pressure in a fluid in equilibrium is the same everywhere. It also states that pressure applied to any part of a fluid contained in a closed system is felt equally in all parts of the fluid. It is formulated by Blaise Pascal. Water distribution in cities, flush tank, hydraulic brake, hydraulic lift, hydraulic press etc are working based on Pascal's law. Fluids are used for pressure transfer in such devices.

Pascal's law, Pressure = Surface Tension/Area

Examples of Pascal's law

• It is based on Pascal's law that it is impossible to reduce the volume of fluids by applying pressure.

• The working principle of a flush tank. 

• The basic law of an excavator.

Note : The melting point of substances which expands on fusion increases with the increase in pressure. For example, Wax. The melting point of substances which contracts on fusion decreases with increase in pressure. For example, Ice.

Pressure Measurement Instruments

Barometer

An instrument called a barometer is used to measure atmospheric pressure. Curiosity about the nature of vacuums led the Italian physicist Evangelista Torricelli to experiment with columns of mercury. From that work came the mercury barometer in 1644, which allowed for the measurement of the varying weight of the atmosphere as the weather changed at a given place. A device for recording atmospheric pressure (barograph) as not invented until 1681, primarily by the English physicist Robert Hooke, who improved on a device developed in 1683 by the English architect Sir Christopher Wren. Scientists use a type aneroid barometer called barograph to record changes in atmospheric pressure. A barograph includes a pen that records the air pressure on a paper chart mounted on a slowly rotating drum. Sudden fall in barometric reading is the indication of storm and the slow fall in barometric reading is the indication of rain. Slow rise in the barometric reading is the indication of clear weather.

Manometer

Manometer is an instrument used to measure the pressure of a gas or vapour. There are several types of manometers. A U-shaped tube with both ends open is the most basic type. The tube contains a liquid, usually mercury, that fills the U's bottom and rises a short distance in each arm. This type involves attaching one arm to the gas whose pressure needs to be monitored. The other arm remains open to the atmosphere. This exposes the liquid to gas pressure in one arm and atmospheric pressure in the other. The liquid rises in the arm of the tube, if the gas pressure is higher than the atmospheric pressure. The user measures the difference between the heights of the liquid in the two arms to determine the pressure of the liquid. The first version of manometer was invented in 1661 by the Dutch physicist Christiaan Huygens.

Work, Power and Energy

1. Work

Work refers to an activity involving a force and movement in the direction of the force. Work depends upon two factors,

(a) force applied and

(b) distance, that the body travels in the direction of force.

Work is the displacement of an object in the direction of the applied force. If an object on the floor is pulled in the direction of the applied force, the work done by that force is positive. The work done by the frictional force exerted by the floor is negative. If a person pushes a metal box without causing the object to move, the work done by that person is zero. If a force of F Newton is applied continuously on an object and it causes a displacement of 'S' meters in the direction of the force, then the work done by that force is,

Work done = Force x Displacement (W = F x S)

Unit of work = Newton meter (Nm) or Joule

In CGS System the unit of work is erg.

When an object is lifted vertically upwards to h meters, the work done against the force of gravity is, 

W = Force x Displacement = mg x h = mgh

Where, mg is the force exerted by the earth on the object and h is the height (Displacement).

SI Unit of Work - The SI unit of work is Joule (J). One joule is the amount of work done to raise an object of mass 1 kg by 1 meter.

♦ 1000 J = 1 kJ

♦ 1 joule = 1 newton meter = 10⁷ erg

The equation for calculating work done when a force is applied at an angle to the direction of motion of the object,

W = FS cosθ

Where, W is the work done; F is force applied; S is Displacement.

♦ F cosθ is the component of the force in the direction of the object's motion.

♦ θ is the angle between the direction of the force and the direction of motion of the object.

♦ The work done is zero, if the force and displacement are at right angles to each other.

♦ The work done is positive, if the force and displacement are in the same direction.

♦ The work done is negative, if the force and displacement are in the opposite direction.

2. Power

Power is the rate of doing work or the rate of using energy. Power is a scalar quantity.

That is, Power = Work/Time

If you do 100 joules of work in one second (using 100 joules of energy), the power is 100 watts. 

Unit of Power - The unit of power is watt or joule/second. It is also measured in horse power.

♦ 1 joule/second = 1 watt

♦ 1 horsepower = 746 watts

♦ 1 kilowatt - 1000 watts

♦ 1 megawatt - 10⁶ watts

The electrical equipments like bulbs, heaters, refrigerators etc are using watts as unit. If a bulb is operated for 10 hours, 1 kilowatt (1KWh) energy would be consumed.

3. Energy

Energy is the capacity to do work. Work is the application of force that causes displacement. Energy has many forms. Thermal energy, chemical energy, electrical energy, radiant energy, nuclear energy, magnetic energy, mechanical energy, heat energy, light energy and sound energy are some of them. One of the fundamental concepts of energy is the law of conservation of energy. Energy cannot be created or destroyed; it can only be transformed into one form to another - this is the law. Law of conservation of energy is developed by Albert Einstein. The term 'Energy' is first used by Thomas Young. The unit of energy is Joule (SI Unit) and Erg (CGS Unit). One Watt Hour is equal to 3600 J. Energy is a scalar quantity. Energy developed in a body due to work done on it is called Mechanical Energy. Mechanical Energy has two forms - Potential Energy and Kinetic Energy.

Potential Energy 

Among the various forms of energy, the most familiar to us is mechanical energy. Cars running and walking are examples of mechanical energy. Mechanical energy is not only found in moving objects. Sometimes, stationary objects also have energy stored in them to move. This type of energy is potential energy. Potential Energy is defined as the energy possessed by a body, by virtue of its position or state of strain. The main reason for the potential energy of objects standing above the ground is the force of gravity. Compressed spring, compressed air and stretched bow possess potential energy due to strain.

Potential Energy = mgh

where, m - mass, g - gravity, h - height (distance between the body and the surface)

Kinetic Energy

Energy of a body due to its motion is called kinetic energy. The change in kinetic energy of an object is equal to the net work done on the object. If the potential energy is given enough, it will be converted into kinetic energy. We generate electricity from the potential energy of water collected in the reservoir of a dam in high areas. The kinetic energy of the water that is brought to the turbines below through a tunnel is converted into electrical energy in the generator. The potential energy of the stored water comes from the sun. The water that evaporates due to the heat of the sun later falls as rain. The heat we use is half potential energy and half kinetic energy. A flying aeroplane possess both Potential Energy and Kinetic Energy. Flowing water, falling objects and fired bullets possess kinetic energy. Kinetic Energy is a Scalar Quantity.

Kinetic Energy = 1/2mv²

where, m - mass, v - velocity

Dimension of Kinetic Energy - [ML²T^-2]

Unit of Kinetic Energy - Joule

Kinetic Energy and Momentum

Momentum, P = mv, Therefore v = P/m

Kinetic Energy, K = 1/2mv² or K = 1/2m(P/m)² = 1/2 x P²/m = P²/2m

Note : 

♦ If the velocity of a moving object is doubled, the kinetic energy increases by a factor of four. Kinetic energy increases as the mass and velocity of the object increase.

♦ For a freely falling body the sum of kinetic energy and potential energy always remains same. As the body falls, its potential energy decreases while the kinetic energy increases by equal amount.

♦ The kinetic energy of an object thrown upward decreases, but its potential energy increases.

♦ The work done by the external force against the gravitational force is mgh. This work is stored as potential energy.

Work-Energy Principle

The Work-Energy Principle states that work is equal to the change in kinetic energy.

The equivalence of Mass and Energy

It was Albert Einstein who proved that mass and energy are the same and that they are related to each other.

E = mc²

Where E = energy, m = mass and c = 3 x 10⁸ m/s = the speed of light in vaccum

Sources of Energy

Sun is the source of energy in Earth. Earth's energy sources can generally be divided into two. Non-renewable and renewable. The first of these is a source of energy that is decreasing over time. They cannot survive innumerable uses. For example, fossil fuels, coal, petroleum, natural gas. These were formed on Earth over millions of years. However, their source is drying up due to continuous mining, so we will have to rely more on renewable energy sources to avoid a future energy crisis. The next are energy sources that do not decrease over time and are constantly being replenished by nature. Some of these are sunlight, wind, rain, tides, biomass, biogas and biofuels. Fuels are sources of energy. Fuels are Non-renewable sources of energy that release heat when burned. Solid fuels include firewood and coal, liquid fuels include diesel, petrol and kerosene, and gaseous fuels include LPG, CNG and hydrogen.

Energy conversions that occur when various devices work

1. Dynamo - mechanical energy => electrical energy

2. Electric generator - mechanical energy => electrical energy

3. Fan - electrical energy => mechanical energy

4. Ironing board - electrical energy => thermal energy

5. Electric bulb - electrical energy => thermal energy, light energy

6. Microphone - sound energy => electrical energy

7. Loudspeaker - electrical energy => sound energy

8. Solar cell and Photo electric cell - light energy => electrical energy

9. Electric motor - electrical energy => mechanical energy

10. Burning candle - chemical energy => thermal energy, light energy

11. Steam engine - thermal energy => mechanical energy

12. Electric heater - electrical energy => thermal energy

13. Electric bell - electrical energy => sound energy

14. Photosynthesis - light energy => chemical energy

15. Heat Engine - heat energy => electrical energy

16. Electric iron - electrical energy => heat energy

Simple Machines

Simple Machine is a device used for performing work by applying force (effort) at a convenient point in a convenient direction to overcome the friction (load) at some other point. Simple Machines help to reduce human effort. Lever, Wheel and axle, Pulley, Inclined plane, Wedge and Screws are the six types of Simple Machines.

Efficiency of a simple machine = Power output/Power input

For an ideal machine, the value of efficiency is one.

Mechanical advantage of a machine = Load/Effort

Types of Simple Machines

1. Lever

One of the six simple machines for work is the lever. It is comprised of a rod or bar that rests and turns on a support called a fulcrum. To lift a load at the opposite end of the rod, a force of effort is exerted at one end. The load arm is the distance between the load and the fulcrum. The effort arm is the distance between the applied force and the fulcrum. A weight can be lifted more easily with the help of a lever. Three classes of lever may be distinguished (a) fulcrum between effort and load, (b) effort between fulcrum and load, (c) load between fulcrum and effort.

2. Wheel and Axle

A mechanical device called wheel and axle is used to lift loads. It is among the most significant invention in history and one of the six simple machines created in ancient times. The simplest wheel and axle consists of a huge wall and a cylinder that are attached to one another and rotate on the same axis. The wheel and axle is a first order lever. The centre of the axle corresponds to the fulcrum and the radius of the axle corresponds to the load arm. The force or effort applied to the arm is reflected in the wheel's radius. Occasionally, a crank is used in place of a wheel. Wheel Barrows and Handcarts can be used as simple machines using the Wheel and Axle system.

3. Pulley

A pulley is a simple machine used to lift heavy things or change the direction of a force. It is made up of a grooved wheel that revolves on an axle or shaft. It makes lifting objects or changing the direction of a pull easier by utilizing a rope or belt that wraps around the wheel. Fixed Pulley, Movable Pulley, Compound Pulley, Block and Tackle Pulley are the different types of Pulleys.

4. Inclined Plane

Inclined plane helps to lift loads to a height with less effort, than when it is lifted straight to the same height. Inclined plane is one of the easiest ways for workers to load heavy logs onto a lorry. This is a method of rolling the logs through two logs on an incline in a lorry. The wedge used by carpenters is a variant of the inclined plane. The nail can be easily driven into the wall because of the inclined plane at its tip. The principle of the inclined plane is also used in the ramp.

5. Wedge

A wedge is an object with two or more sloping surfaces that taper to a point or a sharp edge. Wedges are used to split or pierce materials and is also used to to adjust the positions of heavy materials. Axes, pins, needles, chisels, and knives are all wedges. A wedge must overcome both the resistance of the material and the resistance of friction it is being used on. It might take strong hammer blows to push the wedge forward because of the high overall resistance. The force required to advance a wedge increases with the angle between its surfaces. The wedge cannot be driven into the material if wedge angle is too large. The limiting angle varies from 90° to 180°, depending on the amount of friction acting on the wedges surfaces.

6. Screws

A screw is a simple machine, more precisely a cylinder-wrapped inclined plane. It is frequently used to lift or keep objects together. A screw's spiral threads transform rotational motion into linear motion by functioning as an inclined plane. 

Lever - Types, Examples

Simple machines are devices that make work easier. Simple machines include levers. A lever is a simple machine consisting of a rigid rod pivoted at a fixed point called the Fulcrum. It is used for shifting or raising a heavy load or applying force in a similar way. A body in which a force is felt is called Resistance (R) or load. The force which we exert to lift or displace the load is called Effort (E). Effort is the input force and Resistance/Load is the output force. A long, straight rod of very low mass that can be pivoted about a point on the rod becomes a lever. Strong rods are used to lift heavy objects and reduce labor. This is possible because the rod can move about a fixed point. Levers are rigid rods that move about a fixed point.

Classification of Levers

Based on the position of fulcrum, effort and resistance, levers are classified into three. They are,

First Order Lever - Fulcrum comes in between resistance and effort is First Order Lever.

Eg - Balance, Nail Puller, See-Saw, a pair of scissors, Crowbar, Cutting Player, Pulley, Lawn mower etc.

Second Order Lever - Resistance comes in between effort and fulcrum is Second Order Lever.

Eg - Wheel barrow, nut craker, lemon squeezer, Paper cutter, Bottle Opener etc.

Third Order Lever - Effort is between resistance and fulcrum.

Eg - Icetongs, fishing rod, shovel, screw driver, stapler, hook etc.

If fulcrum is indicated as 'f', effort as 'e' and resistance as 'r', we can explain levers simply as follows.

• The position of f is in between 'r' and 'e' in first order lever.

• The position of r is in between 'f' and 'e' in second order lever.

• The position of e is in between 'f' and 'r' in third order lever.

Compound Lever

The resistance from one lever in a lever system acts as an effort on the next lever. The force applied in this way is transferred from one lever to the next. A compound lever is a simple machine that works on this principle. Train Breakers and Piano Keys are examples of Compound Levers. Malleus, Incus and Stapes are three bones in the middle ear. These work on the principle of Compound Lever. Nail Cutter, Cycle and Sewing Machine are also examples of Compound Levers.

Lord Arm and Effort Arm

Lord Arm is the distance from fulcrum to resistace and Effort Arm is the distance from fulcrum to effort.

Waves - Types, Examples, Properties

A wave is a disturbance which propagates energy from one place to other without the transport of matter. A simple experiment will show how waves carry energy but not matter. First have two boys hold the ends of a rope. When one boy moves his end of the rope up and down sharply, energy passes from one section to the next as a wave. Each part of the rope is set into motion as the wave passes, but the rope itself does not move forward with the wave. The boy holding the other end will feel the energy carried by the wave move his hand. Next, have one boy throw a ball to the other. The catcher feels some of the energy used in throwing the ball. But unlike the wave, the matter - that is, the ball moves forward. As the ball moves, it carries the energy with it. Waves on a rope or water are familier examples of waves, but many other waves move around us all the time. For example, the sound of people travels to our ears as waves.

Types of Waves - Mechanical Waves and Non Mechanical Waves

1. Mechanical waves:

A wave which needs a medium in order to propagate itself. There are Two types of Mechanical Waves - Transverse wave and Longitudinal wave. The property which distinguishes transverse waves from longitudinal waves is polarization. Polarization is a property of waves that can oscillate with more than one orientation. 

i. Transverse Waves

Transverse waves are the waves in which the particles of the medium vibrate perpendicular to the direction of propagation of the wave. Transverse waves travel in the form of crests and troughs while longitudinal wave travels in the form of compressions and rarefactions. Wave on a rope and waves on the surface of water are transverse. Examples of transverse waves are Water waves, Light waves, Secondary waves (seismic S-waves), Stringed instruments, Torsion wave etc.

ii. Longitudinal Wave

Longitudinal waves are the waves in which the particles of the medium vibrate parallel to the direction of propagation of the wave. Examples of longitudinal waves are Sound waves, Primary waves (seismic P-waves), Compression wave etc.

Non-Mechanical Waves

Non-mechanical waves are those that do not require a medium to propagate. These kinds of waves can also travel through a vacuum. These possess a transverse nature. Matter Waves and Electromagnetic Waves are examples of Non Mechanical Waves.

i. Matter Waves

Any moving object can be described as a wave. When a stone is dropped into a pond, the water in the pond is disturbed from its equilibrium positions as the wave passes. it returns to its original equilibrium position after the wave has passed.

ii. Electromagnetic Waves

Electromagnetic waves are related patterns of electric and magnetic force. They are generated by the oscillation of electric charges. Electromagnetic waves are transverse in nature and travel with the speed of light in vaccum. The simplest electromagnetic waves are plane waves. They move through space in straight lines. The strength of the wave varies in space and time with alternating crests and troughs. The distance from crest to crest is called the wavelength. Building on the experiments of Michael Faraday (England) in 1831 the Scottish mathematician James Clerk Maxwell evolved in 1864 a set of four equations which described the nature of electricity and magnetism. It was not until 1888 that Heinrich Hertz (Germany) discovered radio waves. Other types of electromagnetic waves are visible light, microwaves, gamma rays, ultraviolet rays, infrared waves, Radio waves, light rays, thermal radiation, x-rays, and cosmic rays are some of the examples of electromagnetic waves.

Radio waves - Radio and television programmes travel to our homes as radio waves. Short radio waves are easily reflected by ionosphere. So long distance radio broadcasts use short wave bands. The process of transmission and reception of a radio wave signal between two places not joined through wires is known as wireless radio communication. The television signals are not reflected by ionosphere so they are reflected easily to earth by using geo-stationary artificial satellites.

Micro waves - Radio waves with frequencies higher than that of TV signals are called microwaves. Microwaves do not bend or spread around the corners of any kind of obstacles coming in their paths. These microwaves are used in Radar to locate the position of enemy's aeroplane during war time. Radio and microwave frequency waves are produced due to the regularly repeated accelerated motion of free electrons in antena or at the transmission station.

UV rays - The majority of the UV radiations coming from the sun are absorbed by the ozone layer.

Infrared rays - The majority of infrared radiations coming from the sun are absorbed by the atmosphere. Infrared radiation is detected by its heating effect. Special photographic films detect infrared radiation and is used to take pictures in dark. Remote control of TV sets contains a tiny infrared transmitters. The heating effect of sunlight is cancel by infrared radiation.

Green House Effect - The heating of earth's surface or atmosphere due to trapping of infrared rays by the carbon dioxide layer in the lower atmosphere is called Green House Effect.

Properties of Waves

i. Amplitude - Amplitude of wave is the maximum displacement of the vibrating particle on either side from the equilibrium position.

ii. Wave Length - Wave Length is the distance between two successive crests or troughs in transverse wave and in longitudinal waves the distance between two consecutive compressions or rarefactions. It is denoted by the Greek letter lambda (λ). Aircraft and Marine broadcasting use wavelength as long as 3000m.

iii. Time Period - Time Period of wave is the total time that a wave takes to complete a single cycle. Time Period is measured in seconds.

iv. Velocity - Velocity of a wave is the speed at which it travels in one medium. Velocity is measured in meters/seconds.

v. Speed - Speed of a wave is the distance at which it travels at a specified amount of time. Wave speed is also related to wave frequency and wavelength. Speed of wave is the product of frequency  and  wavelength.

vi. Frequency - Frequency is the number of complete wave generated per second.

vii. Wave number - Wave number is defined as the number of wave lengths per centimeter.

viii. Reflection - A portion of a wave is thrown back into the original medium when it strikes a surface where two different media are separated.. This property of bouncing of the waves is called Reflection.

Acoustics - Sound and its Characteristics, Types

Acoustics is a branch of classical physics that deals with the study of sound, including its production, transmission, and effects.

Definition of Sound

Sound is a form of energy which produces sensation of hearing. It is produced by the vibration of material objects. A vibrating source, a propagating medium and a receiver namely ear are the elements required for the sensation of hearing. Acoustics is the study of sound. In humans, the larynx is the part of the throat that produces sound. The sound we hear stays in the ear for about a tenth of a second. Sound needs a medium to travel. Sound cannot travel through vacuum and this is the reason for astronauts using radio system to communicate in Space. Also astronaut can't hear his companion at the surface of moon, since there is no medium for sound propagation. Sound travels faster in steel. The velocity of sound in the air is 340 m/s. The velocity of sound is maximum in solids and least in gases. The velocity of sound in moist air is greater than in dry air. Phonogram is a machine used to reproduce sound. The sound was first recorded by Thomas Edison in 1877.

Unit of Sound - Unit used to measure the frequency of sound is hertz (Hz). 1 kilo hertz is equal to 1000 Hz and 1 mega hertz is equal to 10⁶ Hz.

Speeds of Moving Objects based on Sound

The speed of sound depends on the medium the waves pass through. Based on the speed of sound, the speeds of moving objects can be divided into three as subsonic, supersonic and hypersonic. 

i. Subsonic speeds are speeds slower than the speed of sound (less than Mach 1). Mach Number is the unit used to record the speed of Aeroplanes and Missiles. One Mach is equal to 340 m/s or roughly 750 miles per hour. Most aeroplanes have speeds less than this ie, less than the speed of sound in air.

ii. Supersonic speeds are speeds faster than the speed of sound (greater than Mach 1). Supersonic aircrafts produce a loud noise called a sonic boom when they break the sound barrier. The reason for the sound made by a whip swinging in the air is sonic boom.

iii. Hypersonic speeds are much faster than supersonic speeds (more than Mach 5). Rockets and Space shuttles are capable of traveling at hypersonic speeds.

Source of Sound

Sound is produced by the vibration of objects. Sound sources are objects that produce sound. There are three types of sound sources - man-made sound sources, natural sound sources, and artificial sound sources. Examples of man-made sound sources include drums and flutes. Examples of natural sound sources include cymbals, thunder, and waterfalls. The sound emitted by a sound source is the sum of the many parts associated with the source. However, each sound source has a major part that vibrates to produce sound.

Limits of Audibility 

Sounds with frequencies above 100,000 Hz are also produced in nature due to the vibration of objects. Humans cannot hear all frequencies of sound. That is, there is a limit to the frequency of sound that humans can hear. For a person with normal hearing, the lower limit of audible sound is about 20 Hz and the upper limit is about 20,000 Hz. Sound with frequencies below 20 Hz is called infrasonic, and sound with frequencies above 20,000 Hz is called ultrasonic. 

A Galton whistle is a whistle that produces a high-frequency sound that humans cannot hear. A Galton whistle is a whistle used for dog training. Dogs have a hearing range of 40 Hz to 60 KHz. The sound emitted by the Galton whistle is about 30,000 Hz. 

Hearing range (lowest - highest) Hz

■ Elephant (16 - 12000 Hz)

■ Goldfish (20 - 3000 Hz)

■ Cow (23 - 35000 Hz)

■ Dog (40 - 60000 Hz)

■ Cat (45 - 64000 Hz)

■ Horse (55 - 33500 Hz)

■ Hen (125 - 2000 Hz)

■ Rat (1000 - 91000 Hz)

■ Bat (2000 - 123000 Hz)

Doppler Effect

The Doppler effect is the phenomenon of a change in the frequency of sound due to the relative motion of the sound source or the observer. The frequency of the sound increases as the sound source approaches the source and decreases as it moves away from the source. The Doppler effect has been observed in both sound and light. The Doppler effect was discovered by Christian Doppler. The Doppler effect is used to measure the speed of submarines and aircraft.

Persistence of Hearing

Persistence of hearing is the phenomenon in which the sound we hear remains in our ears for a short time. The human hearing persistence is 1/10 of a second. The vocal cords are the part of the body responsible for producing sound in humans. The three characteristics of sound are loudness, stability, and quality.

Permitted noise limits

■ Commercial area - Day (65dB), Night (55dB)

■ Industrial area - Day (75dB), Night (70dB)

■ Residential area - Day (55dB), Night (45dB)

■ Silent area - Day (50dB), Night (40dB)

■ Hospital - 40 dB

Characteristics of Sound

Sounds are distinguished from each other by pitch (frequency), loudness (intensity) and quality. Some characteristics of sound are as follows.

i. Frequency

In longitudinal waves, particles in the medium vibrate in the same direction as the wave, creating regions of high pressure (compression) and low pressure (rarefactions). Frequency is the number of periodic compressions and rarefactions that occur every second as the sound wave travels through the medium. If an object is allowed to vibrate freely, it will vibrate at its own specific frequency. This frequency is called the natural frequency. The length, thickness, tensile strength, and nature of the object are factors that affect its natural frequency. Hertz is the unit of Frequency. Forced vibration is the process by which a vibrating object causes another object to vibrate at the same frequency as the object that is causing the vibration. 

ii. Loudness/ Intensity

The intensity or loudness of a sound is the vibration of the eardrum. Loudness depends on the frequency of the vibration and the sensitivity of the ear. As the frequency of the vibration increases, the loudness increases. As the frequency of the vibration decreases, the loudness decreases. The intensity of sound increases with increase in the density of the medium. The decibel (dB) is the unit of intensity (loudness) of sound. The decibel (dB) is the smallest unit of the bel. The intensity of polite conversation is 40dB - 50dB. During night the allowed intensity of sound in a hospital area is 40dB. The normal level of sound is 60 to 120dB. The sound above 120dB is painful to ears. Audiometers and decibelmeters are instruments used to measure the loudness of sound. The decibel unit for loudness of sound is named in honor of the scientist Alexander Graham Bell.

Sounds and intensity

■ Barely audible sound - 0-10 db (decibel)

■ Breathing sound - 10 db

■ Clock ticking sound - 30 db

■ Human voice - 60-65 db

■ Telephone bell - 70 db

■ Television, alarm clock - 75 db

■ Vacuum cleaner - 60-80 db

■ Motorcycle - 70-80 db

■ Motor horn - 80 db

■ Noise pollution - Above 90 dB

■ Thunder - 100-110 db

■ Lion roar - 110-120 db

■ Airplane - 120 db

■ Gunshot - Above 120 dB

■ Hearing loss - Above 120 db

■ Jet - 120-140 db

■ Rocket - 170 db

iii. Reflection

Reflection is the phenomenon used in Sonar. SONAR (Sound Navigation and Ranging) is a method of locating under water objects by transmitting a high frequency sound (ultrasonic sound) pulse and detecting or receiving it using a detector (converts ultrasonic waves to electrical signals) after reflected from object. This method can be used to determine the depth of water at a location.

iv. Pitch

Pitch is the shrillness of a sound. The shrillness of a sound is related to the frequency. As the frequency increases, the shrillness of the sound increases. The voice of women and children has more pitch. The female voice has more pitch and the male voice has less pitch. Similarly, the voice of a cuckoo has more pitch and the roar of a lion has less pitch. Pitch is of two types - high pitch and low pitch. The special sound made by chalk on a board at times and the whistling sound are examples of high pitch. The growling of dogs and the sound of thunder are examples of low pitch. Bass is a set of low-pitched sound waves and Treble is a set of high-pitched sound waves. Beats are the fluctuations in sound that occur when two objects with slightly different frequencies vibrate at the same time. The tuning fork was invented by John Shore.

v. Quality

Quality help to distinguish different sound sources that produce the same constant and loud sound. Qualities help to distinguish the sound between two people or between two musical instruments. We can recognise our friends from their voices due to the quality of sound.

vi. Music

Sound that is produced with regular vibrations and is pleasant to listen to is called music. The seven tones and their frequency in music is Sa - 256 Hz, Ri - 288 Hz, Ga - 320 Hz, Ma - 341 Hz, Pa - 384 Hz, Da - 427 Hz, Ni - 480 Hz.

vii. Noise

Noise is the sound caused by unpleasant and irregular vibrations.

viii. Echo

Echo is a reflected sound that is heard very clearly. For the production of echo there should be a minimum distance of 17m between us and the reflecting surface in air. In water, it is 70m. The distance may change depending on the ambient temperature. The reason why movie theater walls are made rough is to avoid echo. Catacoustics is the branch of acoustics dealing with echoes and reflected sounds.

ix. Reverberation and Multiple Reflection of Sound

The reverberation of sound in a hall results due to continued Reflection. The continuous reflection of sound by hitting different objects is known as Multiple Reflection of Sound. Multiple Reflection of Sound is a sound phenomenon that helps the curved sound boards placed behind the stages to spread the sound to all parts of the hall. Reverberation is the continuous sound that occurs as a result of Multiple Reflection of Sound. Gol Gumbaz in Karnataka is an indian creation that uses the reflection feature of sound.

Acoustics of Buildings - Acoustics of Buildings is the science that deals with the things that need to be considered to design sound within buildings so that it can be heard clearly.

x. Resonance

Resonance occurs when the natural frequency of a vibrating object and the natural frequency of the object being vibrated are the same. The object being vibrated is at its maximum, so it vibrates when it is in resonance. Resonance is the acoustic phenomenon that causes window bars to shake during a thunderstorm.

xi. Speed

The speed of sound is the speed at which sound waves travel through various materials. The Speed of Sound  at Atmospheric Temperature in various mediums are as follows.

1. Air - 340 m/s

2. Sea Water - 1531 m/s

3. Pure Water - 1498 m/s

4. Aluminium - 6420 m/s

5. Iron - 5950 m/s

6. Steel - 5960 m/s

7. Glass - 3980 m/s

8. Helium - 965 m/s

9. Nickel - 6040 m/s

10. Brass - 4700 m/s

11. Ethanol - 1207 m/s

12. Methanol - 1103 m/s

13. Hydrogen - 1284 m/s

14. Oxygen - 316 m/s

15. Sulphur Di Oxide - 213 m/s

Types of Sound waves

Sound waves are longitudinal waves. Sound consists of waves of alternate compression and rarefaction that transmit kinetic energy through a medium. They are generally classified into three types: audible, infrasonic, and ultrasonic. 

i. Infrasonic sound waves 

Infrasonic sound waves have frequencies less than 20 Hz and are inaudible to humans. They are lower than the lowest limit of human hearing. Earthquake waves are Infrasonic sound waves. Snakes can receive infrasonic sounds. Seismic waves are Infrasonic. Seismic waves are waves that travel through the Earth's crust as a result of earthquakes, volcanic eruptions, and volcanic eruptions. Seismology is the study of seismic waves. Primary Waves/P waves, Secondary Waves/S waves, and surface waves are subwaves of seismic waves. Primary Waves/P waves have high velocity than other Seismic waves. The Richter Scale is a tool used to determine the intensity of earthquakes. The magnitude of an earthquake is determined by the magnitude of the amplitude on the seismograph. Rayleigh Waves and Love Waves are the surface waves that cause the main damage caused by earthquakes.

ii. Audible sound waves 

Audible sound waves are those within the range of human hearing. The audible frequency of human ear is from approximately 20 Hz to 20,000 Hz. Human sounds are audible sound waves. When we speak, the vibration of vocal cords results in the production of sound. Some examples of audible sound waves are, (1) when a harmonium is played, the sound is produced by the vibration of the reeds, (2) By the vibration of the air column, sound is produced in a flute.

iii. Ultrasonic sound waves

Ultrasonic sound waves, on the other hand, have frequencies above 20,000 Hz and are also inaudible. Ultrasonic waves are waves used to clean spiral tubes, irregularly shaped machine parts, electronic components, etc. Echocardiography is the process of taking pictures of the heart using ultrasonic waves. Ultrasonography is a method used to take pictures of internal organs such as the kidneys, liver, gallbladder, and uterus and detect defects in them. Ultrasonic Wave is a wave used to break up small kidney stones. Sonar is a device used to determine the distance, direction, and speed of underwater objects using ultrasonic waves. Bats can fly in the dark because they can generate ultrasonic sound and if there is any hindrance in their way the sound waves get reflected and they can change their direction. This method is known as Echolocation. They use this method to catch insects also.

Sound Equipments

Equipment for generating or using sound includes musical instruments, hearing aids, sonar systems and sound reproduction and broad casting equipment. Many of these use electro-acoustic transducers such as microphones and loud speakers.

• Device used to listen sound under water - Hydrophone

• Device used to measure the speed of an aircraft - Tachometer

• Device used to record the distance traveled by vehicles - Odometer

• Device used to measure the speed of vehicles - Speedometer

• Device used to graphically depict sound - Oscilloscope

• Device used in the laboratory to conduct sound experiments - Sonometer

• Device used to measure distance using sound - Sonar

• Device that converts sound waves into electrical impulses - Microphone

• Device that converts electrical impulses into sound energy - Loudspeaker

• Devices that use the reflection of sound - Megaphone, Stethoscope

Light and Light Phenomena

For centuries scientists disagreed as to whether light consists of corpuscles (minute particles) or has the characteristics of a wave. The corpuscular theory related to light was proposed by Issac Newton in 1675. Newton also discovered that white light is made up of all colours. Wave theory of light was proposed by Dutch physicist and astronomer, Christian Huygens. According to this theory, light is propagated in the form of waves containing compressions and rarefactions. Christian Huygens presented a paper in 1678 in which he set forth his wave theory. The wave theory received support in 1801 by the work of the English physicist Thomas Young. The measurement of length of light waves was made possible by the interferometer which was discovered in the later half of nineteenth century. In the 1860s, the Scottish physicist James Clerk Maxwell unified the fields of electricity, magnetism and optics and proposed the Electromagnetic theory of light. Maxwell described light as a propagating wave of electric and magnetic fields. Maxwell discovered that visible light is a part of electromagnetic spectrum. Heinrich Hertz experimentally demonstrated that light is an electromagnetic wave in 1887. The particle concept was furthered by the quantum theory of Max Planck in 1900. 

Light is an electromagnetic wave behaves as wave and particle. Thus light has dual nature. The speed of light is different in different medium. The speed of light in a vacuum (3 x10⁸ m/s) is the maximum speed an object can achieve in nature. The velocity of light in different medium are explained by Leon Foucault. The speed of light in water is 2.25 x 10⁸ m/s and the speed of light in Diamond is 1.25 x 10⁸ m/s and in glass is 2 x 10⁸ m/s. Vaccum has low light density and Diamond has high light density. The basis for the existence of life on Earth is light from the sun. The light from the sun reaches the earth in 8 minutes 20 seconds (500 seconds) and light from the moon reaches the earth in 1.3 seconds. There is no need of a medium for the light to travel. Augustine Fresnel invented that light is transverse wave. The path of light is called a Ray of Light and the group of rays of light is called a Beam of Light.

Opaque, Transparent and Translucent Substances

i. Substances which do not pass light through them are called Opaque Substances. For example, Paper, Cardboard, Stone

ii. Substances which allow the light to pass through are called Transparent Substances. For example, Glass

iii. The substance which allow a part of incident light to pass through them are called Translucent Substances. For example, Oiled Paper

Sources of Light and Photometry

The branch of physics which deals with the measurement of light emitted by objects is called Photometry. The main measurements in photometry are the luminous intensity of the source, luminous flux, and illuminance of the surface. The SI unit of luminous intensity is Candela (cd). 

Illuminance - If a light source emits one candela of luminous intensity in one steradian solid angle, the luminous flux emitted in that solid angle is known as illuminance (lux). 

The Illuminance emitted (E) by a source having 'I' luminous intensity is, E = I/r²

Where, r is the distance between surface and source.

Luminance - Luminance is a measure used to measure the brightness of a flat reflective surface. The unit of luminance is cd/m². The approximate luminance of a LCD computer is 250 cd/m².

Light Phenomena

The refraction, reflection, diffraction, dispersion, scattering and interference are the phenomenons of light.

i. Refraction: Refraction is the sudden change of direction of light when passing from one transparent substance to another. Waves are refracted when they pass at an angle from one medium into another in which the velocity of light is different. A pencil standing in water looks broken at the water line because light travels slower in water than in air. The amount that a ray of a certain wavelength bends in passing from one medium into another is indicated by the index of refraction (n) between the two mediums for that wavelength. Finding n is a problem in trigonometry. It is a function of the sines of the angles of incidence and refraction: n = sin i/sin r. This constant number is called the Refractive Index. Refractive Index is denoted by the letter 'n'. This is also called as Snell's Law. 

Examples of Refraction, 

(1) Sun can be seen during early sunrise and late sunset are due to refraction. 

(2) The twinkling of stars is due to refraction of light. (The color of stars is due to their temperature)

(3) A pond looks shallow due to refraction. 

(4) When we put a stick in water it seems to be bend. It is due to refraction.

Refractive Index of a medium is defined as the ratio of speed of light in vaccum to the speed of light in the medium. As the temperature of medium increases, the refractive index decreases. Light passes through medium with the same refractive index without any change in its path. The velocity of light is large in a medium which has small refractive index. The object having highest refractive index is Diamond. 

Mediums and Refractive Index

• Air - 1.0003

• Kerosene - 1.44

• Glycerin - 1.47

• Sunflower Oil - 1.47

• Turpentine Oil - 1.47

• Pyrex Glass - 1.47

• Glass - 1.52

When light is incident obliquely from a medium of higher optical density to a medium of lower optical density, the path of the refracted ray deviates from the vertical. When light is incident obliquely from a medium of lower optical density to a medium of higher optical density, the refracted ray approaches the vertical. The critical angle is the angle of incidence at which the angle of refraction becomes 90° when a light ray passes from a medium of higher optical density to one of lower optical density.

Refractive Index and Critical Angle of Medium

• Water - 1.33 and 48.75°

• Crown Glass - 1.52 and 41.14°

• Flint Glass having high Optical Density - 1.62 and 37.31°

• Diamond - 2.42 and 24.41°

The Refractive Index of Various Wavelengths

Color	Wave Length	Crown Glass	Flint Glass
Violet	369.9	1.533	1.663
Blue	486.1	1.523	1.639
Yellow	589.3	1.517	1.627
Red	656.3	1.515	1.622

ii. Reflection: When a ray of light falls on a smooth surface and returns to the same medium, it is called reflection of light. The rays that fall on a surface are called incident rays and the rays that return from the surface are called reflected rays.

iii. Dispersion: Dispersion is the phenomenon of splitting up of light ray into different colours. A rainbow is formed because sunlight is scattered. Dispersion occurs because different colors in white light are refracted to different degrees. When sunlight undergoes dispersion, it separates into seven component colors. These are - violet, indigo, blue, green, yellow, orange and red (VIBGYOR). Red is the color with the longest wavelength. Violet is the color with the shortest wavelength.

For Example, Rainbow

iv. Diffraction: Diffraction is the bending or spreading of light around fine opaque objects. It is also defined as the spreading out of waves of light as it passes through a narrow aperture. Diffraction of light differs from diffraction of sound because diffraction is most evident when the obstacle is about the same size as the wave-length diffracted.

Examples of Diffraction,

(1) The ring around the sun.

(2) The rainbow color seen on a CD

(3) The reason why the edges of the shadows are blurred and irregular (fuzzy uneven edges)

(4) The spreading of light rays towards the screen from a projector in film theatre

v. Interference: Interference is the phenomenon that occurs when two waves meet while travelling along the same medium. It may be constructive or destructive. It is also defined as, when multiple light waves converge at a point, the wavelength of the resulting wave increases or decreases. 

Examples of Interference,

(1) The beautiful colors seen in soap bubbles 

(2) Oilspread water are due to interference.

vi. Scattering: Scattering is the random and partial reflection of light as it passes through a medium. The sky appears blue due to the scattering of light. Scattering is the random and partial change in direction that occurs when light passes through a medium due to dust particles in the atmosphere. The rate of scattering increases as the wavelength of the component colors decreases. The color violet is the most scattered in visible light. Red is the color with the lowest scattering rate. The rate of scattering and the size of the particles are related to each other. Scattering increases as the size of the particles increases. If the size of the particles is greater than the wavelength of the light, the scattering will be the same for all colors. Since there is no atmosphere on the moon, scattering of light is not possible. Therefore, the color of the sky on the moon is black.

Examples of Scattering,

(1) The blue color of the sky and deep sea.

(2) The red color of the horizon at sunrise and sunset.

Scientific Explanation of blue colour of Sky and Ocean 

The scientific explanation of blue colour of sky is given by Rayleigh. So it is also known as Rayleigh Scattering. According to him, the sky generally looks blue because the blue colour of short wave length is scattered more than the red color of longer wavelength. It is true that the violet waves are scattered, even more than the blue. However, the sky does not appear violet because the sunlight is relatively weak in violet light. The scientific explanation of blue colour of ocean is given by CV.Raman. So it is also called as Raman Scattering. CV.Raman got nobel prize for physics in the year 1930 for the discovery of Raman effect.

vii. Total internal reflection: This is a light phenomenon that helps in high-speed communication through optical fibers. If light is going from a denser to rarer medium and the angle of incidence is greater than the critical angle of incidence, then the light incident on the boundary is reflected back in the denser medium, obeying the laws of reflection. Total internal reflection is a light phenomenon used in medicine to view the inside of the body. Total internal reflection is implemented in endoscopy.

Examples of Total internal reflection

(1) Sparkle of diamonds 

(2) Air bubbles in the water to glitter.

viii. Mirage: Mirage is an optical illusion which is observed usually in deserts and highways on hot summer days. The reason for mirage is refraction and total internal reflection. It is common when the ground is heated by the sun. So that the air in contact with the ground is warmer than the air above. A mirage may occur when a person is driving and sees what seems to be a pool of water lying on a hot paved road ahead. But when the person reaches the spot, the water has disappeared or has seemingly moved farther down the road. Mirages may include distant objects that seem to be closer than they truly are. Other objects, such as a mountain or a ship, may seem to float in the sky. Mirages can be seen in deserts, at sea or in the Arctic.

ix. Tyndall Effect

Tyndall Effect is the phenomenon of scattering light by colloidal particle. The phenomenon in which the path of light is visible through the scattering of very small particles as they pass through a colloidal liquid or mixture.

Fluorescence and Photoluminescence

The phenomenon of absorption of light of one wavelength by a substance and then re-emission of light of greater wavelength is known as fluorescence. The phenomenon of emission of light in the visible region after absorbing certain electromagnetic radiations is called Photoluminescence.

Photo electric effect

Photo electric effect is the phenomenon of ejection of electrons from the metal surfaces (sodium, potassium, zinc etc.), when electromagnetic radiations fall upon such metals. Photo electric effect was discovered by Heinrich Hertz. Photo electric effect was explained by Albert Einstein. He got Nobel prize in 1921 for the scientific explanation of photo electric effect.

Quantum Mechanics

Quantum Mechanics is a field of physics that describes the behaviour of matter and light on the atom and the motion of atomic particles. It also explains how atoms absorb and give off energy as light and it clarifies the nature of light. Quantum mechanics goes beyond the limits of classical physics, which is based on the laws formulated by the English scientist Sir Issac Newton. It ranks as one of the major scientific achievements of the 1990's. Quantum mechanics, in addition to its theoretical importance, has contributed greatly to the development of such practical devices as lasers and transistors. It also has enabled scientists to gain a better understanding of chemical bonds and chemical reactions.

Quantum Theory

The long controversy over whether light was a type of wave or was made up of particles was partially answered by the work of the German physicist Max Planck in 1990. Planck proposed that radiation including light, was emitted in small units that he called 'quanta'. The wave length of the radiation could determine the amount of energy in a quantum. His theory later helped explain the behaviour of atoms and nuclei and was verified by the studies of Albert Einstein (U.S) on the photoelectric effect in 1905. In 1913 the Danish physicist Niels Bohr applied quantum theory in explaining the structure of the atoms, stating that when electrons change their orbits only fixed amounts of energy would be involved thus supporting Planck's theory of quanta. Bohr was awarded the Nobel Prize for physics in 1922.

Quantum Optics

Quantum Optics deals with the application of quantum mechanics to optical systems. An optical system  includes lenses, mirrors, reflecting prisms, projection screens, light sources, filters, detectors, dispersing devices, thin films, fibre-optics bundles etc.

Quantum Electrodynamics

Quantum Electrodynamics is a theory concerning the interaction of electrons and electromagnetic radiation. It deals with the properties of electrons, positrons and photons; with these particles mutual interactions and with their interactions with magnetic and electrical fields. Electrons have negative electrical charges. Positrons are electrons with a positive electrical charge. Photons are packets of radiation that can be considered as particles of light. Photons are emitted by, and form, electrons and positrons under certain conditions. These interactions produce changes in charge and other particle properties. Quantum electrodynamics, also called QED, helps physicists predict and calculate these changes with high precision.

Wave Mechanics

The nature of the electron was examined by the French physicist Louis de Broglie and in 1923, using Einstein's formula of energy and mass and planck's quantum theory, he showed that for any particle there should be an associated wave, which he called 'matter waves'. His theory was verified in 1927 by the American physicists Clinton Davisson and Lester Gerner, who noted that under certain circumstances electron beams would cause diffraction patterns, a phenomenon normally associated with waves. De Broglie's work led the Austrian physicist Erwin Schrodinger to devise in 1926 and developed mathematical expressions to explain such phenomena, a system known as wave mechanics. This work put quantum theory on a firm basis and led to the electron microscope.

Optics - Types, Applications

Optics is the branch of physics and engineering that is concerned with the properties of light. It describes how light is produced, how it is transmitted and how it can be detected, measured and used. Light behaves like a wave and a particle, and optics helps us understand this behavior. Optics includes the study of visible light, infrared rays, ultraviolet rays, x-rays, microwave and radio waves. Many instruments, including binoculars, cameras, magnifiers, microscopes, projectors and telescopes, operate according to the principles of optics. All these instruments have optical devices, such as lenses and mirrors, which transmit and control light. Light is detected and measured with instruments called light meters. Ibn-al-Haitham, also known as Alhazen, an Arabic physicist, mathematician and physician was responsible for the development of the science of optics as a result of his studies of the eye and the nature of light. Originally, the term optics was used only in relation to the eye and vision. Later, optical instruments including lenses and other devices for aiding vision began to be developed. The meaning of the term optics eventually became broadened to cover any application of light. 

Types of Optics

There are two main types of Optics - Ray Optics and Wave Optics.

1. Ray Optics 

Ray Optics is also called as geometrical optics. It defines that light travels in straight lines called 'rays'. Ray Optics studies the concepts like - Reflection of light, Refraction, Lenses and mirrors, Total internal reflection and Optical Density.

i. Reflection of light (like in mirrors)

This is the reflection of light hitting a smooth surface. The rays that fall on a surface are called incident rays and the rays that return from the surface are called reflected rays.

ii. Refraction (bending of light in water or glass)

Refraction is the change in the path of a ray of light when it travels between two medium of different densities. The phenomenon of 'mirage' occurs due to refraction.

iii. Mirrors and Lenses

Mirror is any smooth surface that reflects most of the light striking it and Lens is a piece of transparent material that has at least one curved surface.

iv. Total internal reflection (TIR)

This is a light phenomenon that helps in high-speed communication through optical fibers. Examples of Total internal reflection are Sparkle of diamonds and Air bubbles in the water to glitter.

v. Optical Density

Optical Density is a measure of how much the medium affects the speed of light as it passes through it. As the optical density increases, the speed of light decreases. Medium arranged in order of increasing optical density as air < ​​water < glass < diamond. When a ray of light enters a medium with a higher optical density into a medium with a lower optical density at an angle of incidence greater than the critical angle, the ray is reflected back into the same medium without undergoing refraction, which is known as total internal reflection.

2. Wave Optics

Unlike Ray optics, Wave Optics defines the light as a wave. It helps us understand the concepts like diffraction, interference and polarization.

i. Diffraction (Light bends around obstacles)

Diffraction is the bending or spreading of light around tiny opaque objects. The halo around the sun and the rainbow-like color pattern seen on a CD are all due to the diffraction of light.

ii. Interference (When two light waves meet and form patterns)

Interference occurs when more than one light wave reaches the same point and their effects combine. Interference is the cause of the beautiful colors seen in soap bubbles and oil droplets on water.

iii. Polarization (Light vibrates in one direction)

Polarization is a property of light that refers to the direction of oscillation of light waves. Unlike other waves, light waves have oscillations in a specific direction. This direction is known as the polarization of the light.

Fibre Optics

It is a branch of physics based on the transmission of light through transparent fibres of glass or plastic. These optical fibres can carry light over distances ranging from a few centimeters to more than 160 kilometers. Such fibres work individually or in bundles. Some individual fibres measure less than 0.004 millimetre in diameter. Optical fibres uses the principle of total internal reflection for carrying pulses of light from a laser which represents the informations such as computer data, telephonic conversations, television pictures. A optical fibre has much greater information carrying capacity than a copper cable. They have a highly transparent core of glass or plastic surrounded by a covering called a cladding. They were invented in 1955 by the indian physicist Narinder S.Kapany. The invention of the laser in 1960 and of production techniques for glass fibres in 1970 greatly speeded up the development of fibre optics. The application of Fibre Optics includes Internet & Telecom, Medical (Endoscopy), Military Purposes, Broadcasting, Space Communication and so on. 

Applications of Optics

Practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes and lasers.

i. Mirrors

Mirror is any smooth surface that reflects most of the light striking it. Only a small fraction of the light is absorbed by a mirror. In addition to being non-absorbent, a surface must be smooth to about 0.0001 cm to reflect sharp images. Some rough surfaces reflect light, but they scatter it in all directions so that no image is formed. Most mirrors are made by putting a thin layer of silver or aluminium onto a sheet of high-quality glass. The glass supports the mettalic layer and protects its shiny surface. Many mirrors in scientific instruments have the metal coating infront of the glass. A polished sheet of metal-without glass can also serve as a mirror. Images reflected by a mirror vary according to the mirrors shape. There are three principle kinds of mirrors - plane mirrors, convex mirrors and concave mirrors.

ii. Lenses

Lens is a piece of transparent material that has at least one curved surface. Lenses refract light rays and in doing so can form images of an object. The images may be larger, smaller or the same size as the object itself. Scientists sometimes used lenses to concentrate or spread a beam of light. Lenses are an important part of eyes. They enable the eyes to form sharp images of both near and distant objects. Lenses in the form of glasses and contact lenses are used to correct imperfections in eyesight. They are also an essential part of binoculars, cameras, microscopes, projectors, telescopes and other devices.

iii. Telescopes

The first known telescope was invented in 1608 by a Dutch optician named Hans Lippershey. Eventhough the Dutch tried to keep it a secret, Galileo Galilei, the noted italian astronomer, heard about it and by 1610 had improved it for use in astronomy. Because lenses caused a dispersion of light into obscuring rings of colours, Sir Issac Newton (England) in 1668 built a reflecting telescope in which a parabolic mirror magnified an image. In 1757, the english optician John Dolland prepared lenses made of two kinds of glass so that the bothersome spectra were not created; this was an achromatic lens. In 1897 a large 40 inch lens was built in this way. Many larger telescopes have since been built and radio telescopes have been created.

iv. Microscopes

Microscope is an instrument that magnifies extremely small objects so they can be seen easily. It ranks as one of the most important tools of science. Doctors and biologists; for example, use microscopes to examine bacteria and blood cells. Materials scientists and engineers use microscope, to study the crystal structures within metals and alloys and to examine computer chips and other tiny electronic devices. Biology students use microscopes to observe and learn about algae, protozoa and other single-cell organisms. Dutch spectacle maker Zacharias Janssen devised the first compound microscope in 1590 by combining two double convex lenses in a tube.

v. Lasers

Laser is Light Amplification by Stimulated Emission of Radiation. Laser is the surface intense radiation. Laser is a source of intense monochromatic light in the ultraviolet, visible or infrared region of the spectrum. Laser beams are used in the medical field to perform minute operations.

Electromagnetic Spectrum

Electromagnetic Spectrum is the pattern of arrangement of different types of electromagnetic radiations in the order of increasing wavelength (decreasing frequency). The arrangement of radiations in the increasing order of wavelengths is given below.

Cosmic rays < Gamma rays < X-rays < UV rays < Visible light < IR rays < Micro waves < Radio waves.

To be Continued.