Basics of Physics, Applied Physics and Latest Developments

By Dr. Roman Saini

Basics of Physics and Its Applications in Daily Life

Measurement Metric System and Customary System of Measurement:

● The metric system is an internationally adopted decimal system of measurement. It is now known as the International System of Units (SI).

● The metric system uses units such as meter, liter, and gram to measure length, liquid volume, and mass, just as the customary system in many countries use feet, quarts, and ounces to measure these.

● In addition to the difference in the basic units, the metric system is based on 10s, and different measures for length include kilometer, meter, decimeter, centimeter, and millimeter.

● For the sake of uniformity, scientists all over the world have accepted a set of standard units of measurement.

● The system of units now used is known as the International System of Units (SI units). The SI unit of length is a metre.

Symbol - Name - Quantity

● A - Ampere - electric current

● K - kelvin - temperature

● s - second - time

● M - metre - length

● Kg - kilogram - mass

● Cd - candela - luminous intensity

● Mol - mole - amount of substance

● In physics, the motion is a change in position of an object over time.

● Motion is described in terms of displacement, distance, velocity, acceleration, time, and speed.

Types of Motion:

1. Linear Motion:

● Linear motion (also called rectilinear motion) is a one dimensional motion along a straight line. It can be of two types:

○ Uniform linear motion with constant velocity or zero acceleration;

○ Non-uniform linear motion with variable velocity or non-zero acceleration.

Motion

2. Circular Motion:

● In physics, circular motion is a movement of an object along the circumference of a circle or rotation along a circular path.

● It can be uniform, with a constant angular rate of rotation and constant speed, or non-uniform with a changing rate of rotation. Examples of circular motion include:

○ an artificial satellite orbiting the Earth at a constant height,

○ a fan's blades rotating around a hub,

○ a stone which is tied to a rope and is being swung in circles,

○ a car turning through a curve in a race track and so on.

3. Curvilinear Motion:

● The motion of an object moving in a curved path is called curvilinear motion.

● Curvilinear motion describes the motion of a moving particle that conforms to a known or fixed curve.

● A stone thrown into the air at an angle is an example of curvilinear motion.

4. Periodic and Oscillatory Motion:

● A phenomenon, process or motion, which repeats itself after equal intervals of time, is called periodic.

● If a body moves to and from repeatedly about a mean position it is called oscillatory motion.

5. Rotational Motion and Orbital Revolution: ● A rotation is a circular movement of an object around a center (or point) of

rotation. ● If the axis passes through the body's center of mass, the body is said to rotate

upon itself, or spin. ● A rotation about an external point, e.g. the Earth about the Sun, is called a

revolution or orbital revolution, typically when it is produced by gravity. The axis is called a pole.

6. Rolling Motion: ● Rolling is a type of motion that combines rotation and translation of that

object. ● Most land vehicles use wheels and therefore roll for displacement.

7. Projectile motion

● It is a form of motion experienced by an object (a projectile) that is thrown near the Earth's surface and moves along a curved path under the action of gravity.

● This curved path was shown by Galileo to be a parabola.

● The study of such motions is called ballistics, and such a trajectory is a ballistic trajectory.

8. Brownian motion:

● It is the random movement of microscopic particles suspended in a liquid or gas, caused by collisions with molecules of the surrounding medium.

Basics of Physics and Its Applications in Daily Life

Force ● Force is any interaction that, when unopposed, will change the motion of an

object.

● It can be a push or a pull that can cause an object with mass to change its velocity.

● It is measured in the SI unit of newtons and represented by the symbol F.

● Concepts related to force include:

○ Thrust, which increases the velocity of an object;

○ Drag, which decreases the velocity of an object; and

○ Torque, which produces changes in rotational speed of an object.

First Law of Motion:

● Every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force.

● This is normally taken as the definition of inertia.

● Hence, Inertia is the resistance of any physical object to any change in its state of motion. This includes changes to the object's speed, direction, or state of rest.

● The key point here is that if there is no net force acting on an object (if all the external forces cancel each other out) then the object will maintain a constant velocity.

Newton’s Law of Motion

Application of Newton's First Law of Motion:

● The dust in the bed, carpet or clothes remains intact unless you dust off the objects.

● While dusting a carpet, a small jerk is provided so that carpet moves in a forward direction whereas small dust particles due to inertia remain in their position and hence get separated from the carpet.

● If you shake a tree, the stationary fruits will break away and fall down.

● It becomes hard to balance when you get down from a Merry-Go-Round or a bus or a train. The first law of motion dictates that it continues to keep you in motion, but the ground below your feet is stationary.

● You get thrown back when a stationary bus accelerates. This happens because you are initially at rest when the bus starts to move which makes you feel a force backward.

● On the other hand, you get thrown forward when a moving bus stops suddenly. This happens because you were in motion along with the bus and you continue to be in motion though the bus stops.

● In the game of carrom, if you stack the discs one over another and flick the striker hard, then only the bottom most disc is displaced and the rest of the discs remain as they were.

● The Coin drop experiment and pull-the-tablecloth-without-the-dishes trick we’ve seen are all examples of Newton’s first law of motion.

Second Law of Motion:

● Newton's second law states that acceleration of a particle is dependent on the forces acting upon the particle and the particle's mass.

● For a given particle, if the net force is increased, the acceleration is increased.

● For a given net force, the more mass a particle has, the less acceleration it has.

● For a particle of mass m, the net force F on the particle is equal to the mass m times the particle's acceleration a:

F= m * a

Application of Newton's Second Law of Motion:

● More force is required to be given to a car in order to move it at an equal acceleration as compared to the force required to move a bicycle.

● Catching the ball is a very clear example which uses Newton’s second law of motion.

● Professional sportsmen swing their hand back once they catch the ball as it provides the ball more time to lose its speed. This leads to a lesser force which the sportsman has to apply!

● If you kick a rock it probably won’t even budge. But try tossing a pebble in the water and you might just ace it!

Third Law of Motion:

● For every action, there is an equal (in size) and opposite (in direction) reaction.

● Or every action always reacts in the opposite direction.

● If one object applies force on the other, the size of the force on the first object equals the size of the force on the second object.

● The direction of the force on the first object is opposite to the direction of the force on the second object.

● Forces always come in pairs - equal and opposite action-reaction force pairs.

Application of Newton's Third Law of Motion:

● If you sleep on a hard surface, your body might feel pain. It is because the surface exerts an equal and opposite force on you.

Heavier the object, more is the opposite force applied.

● It is difficult to walk on a slippery surface but you can easily do so on a rough surface.

This is because the horizontal component of the force you exert on the floor for pushing it backwards gets a reaction force from the rough ground in terms of friction acting forwards on your feet, but slippery surface lacks this friction.

Therefore, always take small steps on slippery grounds to minimize the horizontal force you exert on it.

● While firing a gun, it recoils. The piston exerts a force on the bullet to propel it, but the reaction from the bullet causes the piston to move back, taking you along with it.

● Ever felt a jerk while batting in cricket, or pain in the leg while kicking a football?

It is because when you exert the force on the ball to hit it hard, the ball also exerts equal force on you and this causes the jerk or pain you feel.

● Whatever force you exert on the cheek, the same force is exerted by the cheek on your palm.

● The birds use action and reaction pair while flying.

The wings push the air downwards, and the air pushes the bird upwards.

● Similarly, the third law of motion helps us swim as we propel ourselves forward and push the water behind us.

● Rocket propulsion is also a good example of Newton’s Third Law.

The exhaust from the rocket pushes the ground and the ground pushes the rocket with equal and opposite force to cause the latter to move forward.

Four Fundamental Forces of Nature

There are four fundamental forces of nature as follows:

1. Gravitational Force

2. Weak Nuclear Force

3. Electromagnetic Force

4. Strong Nuclear Force

1. Gravitational Force :

a. Weakest force; but has an infinite range.

b. It is a universal force; every object in the universe experience this force due to other objects.

c. Larger objects always exert this force on smaller objects.

2. Weak Nuclear Force :

a. Next weakest, but has a short range.

b. It causes radioactive decay and nuclear fusion of subatomic particles.

3. Electromagnetic Force :

a. Stronger, with infinite range;

b. No medium required;

c. Acts between electrically charged particles such as electrons and protons;

d. Attractive for unlike charges (electron and proton) and repulsive for like charges (two electrons or protons).

4. Strong Nuclear Force :

a. Strongest; but has short range;

b. It binds protons and neutrons in an atomic nucleus;

Centripetal and Centrifugal Forces● Centripetal force is the force needed to make an object travel in a circular

path. ● The centripetal force causes acceleration towards the centre of the circle and

this acceleration is called the centripetal acceleration.● When we swing a ball tied to a string, we observe that the ball follows a

circular path. ● But when we let the string slip through our fingers, we observe that the ball

no longer follows a circular path but flies off in a tangential direction. ● The force acting on the ball pulls it towards the centre of the circle. This

force is called the centripetal force.

● Centrifugal force is defined as, “The apparent force, equal and opposite to the centripetal force, drawing a rotating body away from the center of rotation, caused by the inertia of the body”.

Applications of Centrifugal Force:

● Centrifuges are used to separate materials of different weights or densities by spinning action.

● The liquid is rotated in a cylindrical vessel at a high speed with the help of an electric motor.

● The heavier particles move away from the axis of rotation and lighter particles remain nearer to the axis of rotation.

● The spinning drum in a washing machine to separate water from clothes is a centrifuge.

● Centrifuges are used in separating blood cells from plasma. When blood samples are centrifuged, the heavier red cells reach the bottom and lighter white cells go to the top of the tube.

● Wheel of an automobile spins in mud because the centripetal force is not enough to hold the mud on the tyre.

● Cream from milk, sugar from molasses and honey from beeswax are separated by centrifuges in dairy separators.

● If a vehicle moves at very high speed over a curved path, the centrifugal force makes it topple.

This is because the centrifugal force overcomes the frictional force between the road and the tyres of the vehicle.

To prevent this, the curved tracks are always banked. It means that the outer edge of the road is slightly elevated at an angle.

● The centrifugal force keeps the motorcyclist glued to his seat while driving his motorcycle inside the cage.

● In the circus, during the cage of death event, a motorcyclist drives a motorcycle at a high speed on the inner walls of a spherical cage of iron.

But he does not fall off the motorcycle even when he is upside down.

● Pressure is the amount of force applied perpendicular to the surface of an object per unit area.

● So the smaller the area larger the pressure on a surface for the same force.

Pressure

Applications of Pressure :

● The edge of a knife has an extremely small area to create high pressure for the blade to cut through things.

● Football studs have sharp spikes which reduce the area of contact and therefore increase pressure and grip on the track.

● Snow skis are built with a large bottom surface area so that it puts very less pressure on the snow to avoid sinking.

● Good backpacks or school bags have wide shoulder pads to reduce pressure on the shoulder.

Surface Tension

● It is the tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area.

● Surface tension is responsible for the shape of liquid droplets.

● Although easily deformed, droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer.

Applications of Surface Tension:

● Insects like ants and water-spiders are able to walk on the surface of the water.

● Mosquitoes sit and move freely on the surface of stagnant water.

● When we pour oil on the surface of the water it lowers the surface tension of water. Hence the mosquito breed sinks down and perishes.

● When we take a clean glass plate and place a very small amount of mercury on the plane surface, we observe that the mercury assumes the form of a spherical drop.

● If a brush is dipped in water, its bristles spread out. If it is taken out the bristles come closer and cling together.

● When we place a greased sewing needle carefully on a water surface, the sewing needle makes a small depression in the surface and keeps floating even though the density of the needle is very much greater than that of water.

● Soaps and detergents help in cleaning clothes by lowering the surface tension of water so that it readily soaks into pores and soiled areas.

The purpose of applying soap to clothes is to spread it over a large area.

By reducing surface tension we facilitate the liquid to spread over larger surfaces.

● The major reason for using hot water for washing is that its surface tension is lower and it is a better wetting agent.

But if the detergent lowers the surface tension, the heating may be unnecessary.

● In voyage at the high seas, when there are violent waves the sailors pour tins of oil around their boats or ships.

Due to oil, the surface tension of seawater is reduced thereby reducing the height of water waves also.

Friction● Friction is the force that tries to slow down the movement of solids or

fluid layers.

● Any object moving over another object slows down and finally comes to rest even when no apparent external force is applied on it. It is due to the hidden force of Friction.

● Friction is caused by the interlocking of irregularities on the two surfaces in contact.

● Even those surfaces which appear very smooth have a large number of minute irregularities on them.

● The force required to overcome friction at the moment a body starts to move from rest is a measure of static friction.

● On the other hand, the force required to keep an object moving with the same speed is a measure of sliding friction.

● Sliding friction is somewhat smaller than static Friction.

● That's why it's easier to move a box already in motion than to move it from rest.

● When one body rolls over the surface of another body, the resistance to its motion is called the rolling friction.

● It is always easier to roll than to slide a body over another. Therefore rolling friction is even smaller than sliding Friction.

● Similarly, fluids i.e liquids and gases also exert a force of Friction on objects moving through them. This frictional force exerted by fluids is also known as drag.

● The frictional force on an object in a fluid depends on its speed with respect to the fluid, shape of the object and nature of the fluid.

Applications of Friction:

● Friction plays a vital role in our daily life. Without friction we are handicapped.

● We cannot fix a nail in the wood or wall if there is no friction. It is friction which holds the nail.

● A horse cannot pull a cart unless friction furnishes him a secure foothold.

● You can sit on a chair but won't be able to get up without Friction.

● You can't wear your dress, flipper etc without Friction.

● Friction helps you in writing as your pen or pencil won't work on the frictionless surface.

Disadvantages of friction

● The main disadvantage of friction is that it produces heat in various parts of machines. In this way, some useful energy is wasted as heat energy.

● Due to friction, we have to exert more power in machines.

● Due to friction, noise is also produced in machines.

● Due to friction, engines of automobiles consume more fuel which is a loss of money.

● Machine efficiency is also decreased: energy input is lost to heat.

● Forest fires are caused due to friction between branches of trees.

Methods of Reducing Friction

1. Use of Lubricants :

The parts of machines which are moving over one another must be properly lubricated by using oils and lubricants of suitable viscosity.

2. Use of Grease :

Proper greasing between the sliding parts of the machine reduces the friction.

3. Use of Ball Bearing:

In Machines where possible, sliding friction can be replaced by rolling friction by using ball bearings.

4. Design Modification:

Friction can be reduced by changing the design of fast moving objects. The front of vehicles and airplanes are made oblong to minimize friction.

Work

● The concept of work in physics is much more narrowly defined than the common use of the word.

● In our everyday language, work is related to the expenditure of muscular effort, but this is not the case in the language of physics.

● Work is done on an object when an applied force moves it through a distance.

● A person that holds a heavy object does no physical work because the force is not moving the object through a distance.

Work, according to the physics definition, is being accomplished while the heavy object is being lifted but not while the object is stationary.

● Another example of the absence of work is a mass on the end of a string rotating in a horizontal circle on a frictionless surface.

The centripetal force is directed toward the center of the circle and, therefore, is not moving the object through a distance; that is, the force is not in the direction of motion of the object.

Energy● Energy, in physics, is the capacity for doing work. ● It may exist in potential, kinetic, thermal, electrical, chemical, nuclear, or

other various forms. ● After it has been transferred, energy is always designated according to its

nature.● Hence, heat transferred may become thermal energy, while work done may

manifest itself in the form of mechanical energy.● All forms of energy are associated with motion. For example, any given

body has kinetic energy if it is in motion.

● A tensioned device such as a bow or spring, though at rest, has the potential for creating motion; it contains potential energy because of its configuration.

● Similarly, nuclear energy is potential energy because it results from the configuration of subatomic particles in the nucleus of an atom.

Principle of conservation of energy:

● Energy can be neither created nor destroyed but can only be changed from one form to another. This principle is known as the conservation of energy or the First Law of Thermodynamics.

● For example, when a box slides down a hill, the potential energy that the box has from being located high up on the slope is converted to kinetic energy, the energy of motion.

● As the box slows to a stop through friction, the kinetic energy from the box’s motion is converted to thermal energy that heats the box and the slope.

● Energy can be converted from one form to another in various other ways.

● Usable mechanical or electrical energy is, for instance, produced by many kinds of devices, including fuel-burning heat engines, generators, batteries, fuel cells, and magnetohydrodynamic systems.

Sound● Sound is a vibration that typically propagates as an audible wave of

pressure, through a transmission medium such as a gas, liquid or solid.

● The sound waves are generated by a sound source, such as the vibrating diaphragm of a stereo speaker.

● The sound source creates vibrations in the surrounding medium.

● As the source continues to vibrate the medium, the vibrations propagate away from the source at the speed of sound, thus forming the sound wave.

● The matter that supports the sound is called the medium.

● Sound cannot travel through vacuum.

● Note that the particles of the medium do not travel with the sound wave.

Characteristics of Sound Waves:

Amplitude:

● It is the size of the vibration, and this determines how loud the sound is.

● Larger vibrations make a louder sound.

● Amplitude is important when balancing and controlling the loudness of sounds, such as with the volume control on your CD player.

● It is also the origin of the word amplifier, a device which increases the amplitude of a waveform.

Frequency:

● It is the speed of the vibration, and this determines the pitch of the sound.

● Frequency is measured as the number of wave cycles that occur in one second.

● The unit of frequency measurement is Hertz (Hz for short).

● A frequency of 1 Hz means one wave cycle per second.

Speed of sound:

● The speed of sound is the distance travelled per unit time by a sound wave as it propagates through an elastic medium.

● In dry air at 0 °C (32 °F), the speed of sound is 331.2 metres per second.

● At 20 °C (68 °F), the speed of sound is 343 metres per second. ● The speed of sound in an ideal gas depends only on its temperature and

composition. ● In layman’s language, the speed of sound refers to the speed of sound waves

in air. ● However, the speed of sound varies from substance to substance: sound

travels most slowly in gases; it travels faster in liquids; and still faster in solids.

● The ratio of the speed of an object to the speed of sound in a fluid medium is called the object's Mach number.

● Objects moving at speeds greater than Mach 1 are said to be travelling at supersonic speeds.

Reverberation:

● A sound created in a big hall will persist by repeated reflection from the walls until it is reduced to a value where it is no longer audible.

● The repeated reflection that results in this persistence of sound is called reverberation.

● In an auditorium or big hall, excessive reverberation is highly undesirable.

● To reduce reverberation, the roof and walls of the auditorium are generally covered with sound-absorbent materials like compressed fibreboard, rough plaster or draperies.

● The seat materials are also selected on the basis of their sound absorbing properties.

Pitch:

● Pitch is perceived as how "low" or "high" a sound is and represents the cyclic, repetitive nature of the vibrations that make up the sound.

● A high pitch sound corresponds to a high frequency sound wave and a low pitch sound corresponds to a low frequency sound wave.

● Amazingly, many people, especially those who have been musically trained, are capable of detecting a difference in frequency between two separate sounds that is as little as 2 Hz.

● Every sound is placed on a pitch continuum from low to high.

Timbre, Tone, Note and Noise

● The quality or timbre of the sound is that characteristic which enables us to distinguish one sound from another having the same pitch and loudness.

● The sound which is more pleasant is said to be of a rich quality.

● A sound of a single frequency is called a tone.

● The sound which is produced due to a mixture of several frequencies is called a note and is pleasant to listen.

● Music is pleasant to hear and is of rich quality.

● Noise is unpleasant to the ear!

Audio frequency:● An audio frequency or audible frequency is characterized as a periodic

vibration whose frequency is audible to the average human. ● The SI unit of audio frequency is the hertz (Hz). ● The generally accepted standard range of audible frequencies is 20 to

20,000 Hz. ● Frequencies below 20 Hz are generally felt rather than heard, assuming the

amplitude of the vibration is great enough. ● Children below five and some animals, such as dogs can hear up to 25 kHz

(1 kHz = 1000 Hz). ● As people grow older their ears become less sensitive to higher frequencies.

Loudness and Intensity:

● The amount of sound energy passing through a unit area each second is called the intensity of sound.

● We sometimes use the terms “loudness” and “intensity” interchangeably, but they are not the same.

● Loudness is a measure of the response of the ear to the sound.

● Even when two sounds are of equal intensity, we may hear one louder than the other simply because our ear detects it better.

Hearing Aid:

● People with hearing loss may need a hearing aid.

● A hearing aid is an electronic, battery operated device.

● The hearing aid receives sound through a microphone.

● The microphone converts the sound waves to electrical signals.

● These electrical signals are amplified by an amplifier.

● The amplified electrical signals are given to a speaker of the hearing aid.

● The speaker converts the amplified electrical signal to sound and sends to the ear for clear hearing.

Reflection of Sound:

● Sound bounces off a solid or a liquid just like a rubber ball bounces off a wall.

● Like light, the sound gets reflected from the surface of a solid or liquid and follows the same laws of reflection.

● The directions in which the sound is incident and is reflected make equal angles with the normal to the reflecting surface at the point of incidence, and the three are in the same plane.

● An obstacle of large size which may be polished or rough is needed for the reflection of sound waves.

Uses of Multiple Reflection of Sound: ● Megaphones or loudhailers, horns, musical instruments such as trumpets

and shehanais, are all designed to send sound in a particular direction without spreading it in all directions.

● In these instruments, a tube followed by a conical opening reflects sound successively to guide most of the sound waves from the source in the forward direction towards the audience.

● Stethoscope is a medical instrument used for listening to sounds produced within the body, chiefly in the heart or the lungs.

● In stethoscopes, the sound of the patient’s heartbeat reaches the doctor’s ears by multiple reflections of sound.

● Generally, the ceilings of concert halls, conference halls and cinema halls are curved so that sound reaches all corners of the hall after reflection.

● Sometimes a curved soundboard may be placed behind the stage so that the sound, after reflecting from the soundboard, spreads evenly across the width of the hall.

Echo:

● If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later.

● This sound which we hear is called an echo.

● The sensation of sound persists in your brain for about 0.1 s.

● To hear a distinct echo the time interval between the original sound and the reflected one must be at least 0.1s.

● For hearing distinct echoes, the minimum distance of the obstacle from the source of sound must be 17.2 m.

● This distance will change with the temperature of the air.

● Echoes may be heard more than once due to successive or multiple reflections.

● The rolling of thunder is due to the successive reflections of the sound from a number of reflecting surfaces, such as the clouds and the land.

Infrasound and Ultrasound● Sounds of frequencies below 20 Hz are called infrasonic sound or

infrasound. ● Frequencies higher than 20 kHz are called ultrasonic sound or ultrasound. ● Ultrasounds are high frequency waves and can travel along well-defined

paths even in the presence of obstacles. ● Rhinoceroses, whales and elephants produce sound in the infrasound range. ● It is observed that some animals get disturbed before earthquakes.

Earthquakes produce low-frequency infrasound before the main shock waves begin which possibly alert the animals.

Applications of Ultrasound:

Cleaning:

● Ultrasound is generally used to clean parts located in hard-to-reach places, for example, spiral tube, odd shaped parts, electronic components etc.

● Objects to be cleaned are placed in a cleaning solution and ultrasonic waves are sent into the solution.

● Due to the high frequency, the particles of dust, grease and dirt get detached and drop out.

● The objects thus get thoroughly cleaned.

Flaw detection:

● Ultrasounds can be used to detect cracks and flaws in metal blocks.

● Metallic components are generally used in the construction of big structures like buildings, bridges, machines and also scientific equipment.

● The cracks or holes inside the metal blocks, which are invisible from outside reduces the strength of the structure.

● Ultrasonic waves are allowed to pass through the metal block and detectors are used to detect the transmitted waves. Even if there is a small defect, the ultrasound gets reflected back indicating the presence of the flaw or defect.

● Ordinary sound of longer wavelengths cannot be used for such purposes as it will bend around the corners of the defective location and enter the detector.

Ultrasonography:

● In this technique, the ultrasonic waves travel through the tissues of the body and get reflected from a region where there is a change of tissue density.

● These waves are then converted into electrical signals that are used to generate images of the organ.

● These images are then displayed on a monitor or printed on a film.

● A doctor may image the patient’s organs such as the liver, gallbladder, uterus, kidney, etc.

● It helps the doctor to detect abnormalities, such as stones in the gall bladder and kidney or tumours in different organs.

● Ultrasonography is also used for examination of the foetus during pregnancy to detect congenital defects and growth abnormalities.

● Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.

● Ultrasound may be employed to break small ‘stones’ formed in the kidneys into fine grains. These grains later get flushed out with urine.

Bats:

● Bats search out prey and fly at night by emitting and detecting reflections of ultrasonic waves.

● The high-pitched ultrasonic squeaks of the bat are reflected from the obstacles or prey and returned to the bat’s ear.

● The nature of reflections tells the bat where the obstacle or prey is and what it is like.

Other Animals:

● Ultrasound is produced by dolphins.

● Porpoises also use ultrasound for navigation and location of food in the dark.

● Moths of certain families have very sensitive hearing equipment. These moths can hear the high frequency squeaks of the bat and know when a bat is flying nearby, and are able to escape capture.

● Rats also play games by producing ultrasound.

SONAR

● The acronym SONAR stands for SOund Navigation And Ranging.

● Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

Working of SONAR:

● Sonar consists of a transmitter and a detector and is installed in a boat or a ship.

● The transmitter produces and transmits ultrasonic waves.

● These waves travel through water and after striking the object on the seabed, get reflected back and are sensed by the detector.

● The detector converts the ultrasonic waves into electrical signals which are appropriately interpreted.

● The above method is called echo-ranging.

● The sonar technique is used to determine the depth of the sea and to locate underwater hills, valleys, submarine, icebergs, sunken ship etc.

Electricity

Electric charge:

● Two of the tiny particles that make up atoms — protons and electrons — are the bearers of electric charge.

● There are two types of charges:

○ Positive and

○ Negative

● Protons have a positive charge.

● Electrons have a negative charge.

Electric current: ● It refers to the flow of the electric charge carried by electrons as they

jump from atom to atom. Atoms that let current flow easily are called conductors, whereas atoms that don’t let current flow easily are called insulators.

● Metals like copper, silver, and gold are good conductors.

● Insulators serve a very important purpose: they prevent the flow of electrons. Popular insulators include glass, rubber, plastic, and air.

● An electric circuit is a closed loop made of conductors and other electrical elements through which electric current can flow.

● For example, a very simple electrical circuit consists of three elements: a battery, a lamp, and an electrical wire that connects the two.

Volt:

● The pressure that is put on free electrons that causes them to flow is known as electromotive force (EMF).

● A volt is the amount of electromotive force required to push a current of one ampere through a conductor with a resistance of one ohm.

Ampere:

● The ampere defines the flow rate of the electric current.

● For instance, when one coulomb charge flows past a given point on a conductor in one second, it is defined as a current of one ampere.

The Ohm:

● The ohm is the unit of resistance in a conductor.

● Three things determine the amount of resistance in a conductor: its size, its material (e.g., copper or aluminum) and its temperature.

● A conductor’s resistance increases as its length increases or diameter decreases.

● The more conductive the materials used, the lower the conductor resistance becomes.

● Conversely, a rise in temperature will generally increase resistance in a conductor.

Ohm’s Law:

● Ohm’s Law defines the correlation between electric current (I), voltage (V), and resistance (R) in a conductor.

● Ohm’s Law can be expressed as:

V = I × RWhere: V = volts, I = amps, R = ohms

Electrostatic force (also called Coulomb’s law):

● It is a force that operates between charges.

● It states that charges of the same type repel each other, while charges of opposite types are attracted together. Opposites attract, and likes repel.

Static electricity:

● Static electricity exists when there is a build-up of opposite charges on objects separated by an insulator. Static discharges can be harmful.

● When the charges do find a means of equalizing, a static discharge occurs.

● Charges equalizing through an air gap can result in a visible shock as the travelling electrons collide with electrons in the air, which become excited and release energy in the form of light.

● Example - lightning: when a cloud system gathers enough charge relative to earth’s ground, the charges will try to equalize. As the cloud discharges, massive quantities of positive (or sometimes negative) charges run through the air from the ground to cloud causing lightning.

Current Electricity:

● Current electricity is the form of electricity which makes all of our electronic gizmos possible.

● Current electricity is a constant flow of electrons.

● There are two kinds of current electricity:

○ Direct current (DC) - electrons move in one direction

Batteries produce direct current.

○ Alternating current (AC) - electrons flow in both directions.

Power plants produce AC electric current.

Electric Fields: ● Electric fields describe the pulling or pushing force in a space between

charges. ● Compared to Earth’s gravitational field, electric fields have one major

difference: while Earth’s field generally attracts only other objects of mass, electric fields push charges away just as often as they attract them.

Electric Potential Energy: ● When we harness electricity to power our circuits, gizmos, and gadgets,

we’re really transforming energy. ● Electronic circuits must be able to store energy and transfer it to other forms

like heat, light, or motion. The stored energy of a circuit is called electric potential energy.

Electric power:

● Electric power is the rate at which energy is transferred.

● It’s measured in terms of joules per second (J/s) – a watt (W).

● All electronic components transfer energy from one type to another.

● Some energy transfers are desired: LEDs emitting light, motors spinning, batteries charging.

● Other energy transfers are undesirable, but also unavoidable. These unwanted energy transfers are power losses, which usually show up in the form of heat. Too much power loss – too much heat on a component – can become very undesirable.

Magnetism● Magnetism is a phenomenon associated with magnetic fields, which arise

from the motion of electric charges. ● Magnetic field is the region in the neighbourhood of a magnet, electric

current, or changing electric field, in which magnetic forces are observable. ● Magnetic fields such as that of the Earth cause magnetic compass needles

and other permanent magnets to line up in the direction of the field. ● Magnetic fields force electrically charged particles to move in a circular or

helical path. ● Evidence for the presence of a magnetic field is the magnetic force on

charges moving in that field.

● This force deflects the particles without changing their speed.

● The deflection can be observed in the torque on a compass needle that acts to align the needle with the magnetic field of Earth.

● The magnetic field is sometimes referred to as magnetic induction or magnetic flux density; it is always symbolized by B.

● Magnetic fields are measured in units of Tesla (T).

● The most common source of magnetic fields is the electric current loop. It may be an electric current in a circular conductor or the motion of an orbiting electron in an atom.

Diamagnetism:

● Diamagnetism appears in all materials and is the tendency of a material to oppose an applied magnetic field, and therefore, to be repelled by a magnetic field.

● Materials called diamagnetic are those that lay people generally think of as non-magnetic.

● They include water, wood, most organic compounds such as petroleum and some plastics, and many metals including copper, mercury, gold etc.

Paramagnetism:

● It is a form of magnetism whereby certain materials are weakly attracted by an externally applied magnetic field.

● In contrast with this behavior, diamagnetic materials are repelled by magnetic fields and form induced magnetic fields in the direction opposite to that of the applied magnetic field

Ferromagnetism:

● It is the basic mechanism by which certain materials (such as iron) form permanent magnets, or are attracted to magnets.

● Ferromagnetism is the strongest type of magnetism.

● It is the only one that typically creates forces strong enough to be felt, and is responsible for the common phenomena of magnetism in magnets encountered in everyday life.

● Ferromagnetism only occurs in a few substances; the common ones are iron, nickel, cobalt, their alloys, and some alloys of rare-earth metals.

● Every ferromagnetic substance has its own individual temperature, called the Curie temperature, or Curie point, above which it loses its ferromagnetic properties.

● An everyday example of ferromagnetism is a refrigerator magnet used to hold notes on a refrigerator door.

Electromagnet: ● An electromagnet is a type of magnet in which the magnetic field is

produced by an electric current. ● The magnetic field disappears when the current is turned off.

● The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding.

● However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field.

● Electromagnets are widely used as components of other electrical devices, such as motors, generators, relays, solenoids, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment.

● Electromagnets are also employed in the industry for picking up and moving heavy iron objects such as scrap iron and steel.

Optics

Sources of Light:

● The objects that emit light are called as sources of light.

● Sources of light are of two types natural and artificial.

● The sun is the primary and the natural source of light.

● Some of the man-made objects also produce light. These are called artificial sources of light.

Luminous and Non-luminous Objects:

● Bodies like Sun that emit light on their own are called luminous bodies.

● Objects like table, chair etc. do not emit light on their own and are called non-luminous bodies.

Transparent, Opaque and Translucent Objects:

● If we cannot see through an object at all, it is an opaque object.

● If you are able to see clearly through an object, it is allowing light to pass through it and is transparent.

● There are some objects through which we can see, but not very clearly. Such objects are known as translucent.

Darkness and Shadows:

● When certain objects are placed in front of sunlight or torchlight, a shadow is formed behind the object.

● Since the object placed in the path of light does not allow light to pass through it, there is no possibility of light rays to go behind the object. Hence that region is dark. This is because light travels in a straight line.

● All objects do not cast a shadow, only opaque objects cast a shadow.

● We need a source of light, an opaque object and a screen (wall, floor, building etc. act as a screen) to cast a shadow.

Reflection, Refraction, and Diffraction:● Reflection is the change in direction of light at an interface between two

different media so that the light returns into the medium from which it originated.

● If the surface is smooth it is called regular reflection and if it is rough, it is called diffused reflection.

● Refraction of waves involves a change in the direction of waves as they pass from one medium to another.

● Refraction, or the bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves.

● Diffraction is the slight bending of light as it passes around the edge of an object or a narrow slit.

● In the atmosphere, diffracted light is actually bent around atmospheric particles like tiny water droplets found in clouds.

● Silver lining sometimes found around the edges of clouds or coronas surrounding the sun or moon is due to diffraction.

Laws of Reflection:

● The law of reflection governs the reflection of light-rays off smooth conducting surfaces, such as polished metal or metal-coated glass mirrors.

● Consider a light-ray incident on a plane mirror.

● The law of reflection states that the incident ray, the reflected ray, and the normal to the surface of the mirror all lie in the same plane.

● Furthermore, the angle of reflection r is equal to the angle of incidence i.

● Both angles are measured with respect to the normal to the mirror.

i r

Reflec

ted R

ayIncident Ray

Normal

Reflection from Mirrors:

Plane mirror:

● A plane mirror is a mirror with a flat (planar) reflective surface.

● One surface of the glass is polished to a high degree of smoothness forming the front surface of the mirror.

● The back surface is silvered that is then painted with silver or mercury or some opaque material.

● A plane mirror makes an image of objects in front of it; these images appear to be behind the plane in which the mirror lies.

● The image formed by a plane mirror is always virtual, upright, and of the same shape and size as the object it is reflecting.

Spherical mirrors:● A spherical mirror is a mirror which has the shape of a piece cut out of a

spherical surface. ● The surface may be either convex (bulging outwards) or concave (bulging

inwards).Convex mirrors: ● A convex mirror, diverging mirror, or fish eye mirror is a curved mirror in

which the reflective surface bulges toward the light source.

● Convex mirrors reflect light outwards, therefore they are not used to focus light.

● Such mirrors always form a virtual image.

● Images formed by these mirrors cannot be projected on a screen since the image is inside the mirror.

● The image is smaller than the object but gets larger as the object approaches the mirror.

● Since everything appears smaller in the mirror, they cover a wider field of view than a normal plane mirror does.

● A collimated (parallel) beam of light diverges (spreads out) after reflection from a convex mirror, since the normal to the surface differs with each spot on the mirror.

Uses of convex mirrors:● The passenger-side mirror on a car is typically a convex mirror.

● Convex mirrors are preferred in vehicles because they give an upright, though diminished, image.

● Also, they provide a wider field of view as they are curved outwards. ● These mirrors are often found in the hallways of hospitals, hotels, schools,

stores, and apartment buildings. They are useful for people accessing the hallways, especially at locations having blind spots or where visibility may be limited.

● They are also used on roads, driveways, and alleys to provide safety for motorists where there is a lack of visibility, especially at curves and turns.

● Convex mirrors are used in some automated teller machines as a simple and handy security feature, allowing the users to see what is happening behind them.

Concave mirrors:

● A concave mirror, or converging mirror, has a reflecting surface that bulges inward (away from the incident light).

● Concave mirrors reflect light inward to one focal point. They are used to focus light.

● Unlike convex mirrors, concave mirrors show different image types depending on the distance between the object and the mirror.

● These mirrors are called "converging mirrors" because they tend to collect light that falls on them, refocusing parallel incoming rays toward a focus.

Uses of concave mirrors:

● Concave mirrors are used in reflecting telescopes.

● They are also used to provide a magnified image of the face for applying makeup or shaving.

● In illumination applications, concave mirrors are used to gather light from a small source and direct it outward in a beam as in torches, headlamps and spotlights, or to collect light from a large area and focus it into a small spot, as in concentrated solar power.

Refraction by spherical lenses:● A lens is a transparent piece of glass or plastic with at least one curved

surface.● A lens works by refraction: it bends light rays as they pass through it. So

they change direction. ● That means the rays seem to come from a point that's closer or further away

from where they actually originate—and that's what makes objects seen through a lens seem either bigger or smaller than they really are.

● There are two main types of lenses, known as ○ Convex (or converging) and

○ Concave (or diverging).

Convex lenses:

● In a convex lens (sometimes called a positive lens), the glass (or plastic) surfaces bulge outwards in the center giving the classic lentil-like shape.

● A convex lens is also called a converging lens because it makes parallel light rays passing through it bend inward and meet (converge) at a spot just beyond the lens known as the focal point.

● When light passes through a converging lens, light refracts.

● If the incident rays are parallel to the principal axis, in this case the line that passes through the center of the lens, the refracted rays will all meet in one point known as the principal focus.

● A magnifying glass is a convex lens which produces a magnified image of an object.

Uses of Convex Lenses:

● Used as a simple magnifying lens

● The convex lens is also used in cameras and projectors because it focuses light and produces a clear and crisp image.

● It is used to correct Hypermetropia or long-sightedness.

● It is also used in other magnifying devices such as microscopes and telescopes.

Concave lenses:

● Concave lenses are thinner at the middle.

● Rays of light that pass through the lens are spread out (they diverge).

● A concave lens is a diverging lens.

● When parallel rays of light pass through a concave lens the refracted rays diverge so that they appear to come from one point called the principal focus.

Uses of concave lenses:● Binocular and telescope manufacturers install concave lenses in or before

the eyepieces to help focus images more clearly for the viewer. ● Camera manufacturers use combinations of concave and convex lenses to

improve the quality of photographs.● Concave lenses are used on flashlights to magnify the light produced by the

bulb.● Various types of medical equipment, scanners and CD players use laser

beams. Small concave lenses can widen a laser beam to precisely access a specific area.

● In Door viewers or peepholes, the view is created through the use of one or more concave lenses inside the device.

Dispersion of light by glass prisms:

● Visible light, also known as white light, consists of a collection of component colors.

● These colors are often observed as light passes through a triangular prism.

● Upon passage through the prism, the white light is separated into its component colors - red, orange, yellow, green, blue and violet.

● The separation of visible light into its different colors is known as dispersion.

● Each color is characteristic of a distinct wave frequency and different frequencies of light waves will bend differently upon passage through a prism.

● The deviation in the path of the light is inversely proportional to the wavelength.

● The red color having the maximum wavelength deviates the least and forms the upper part of the spectrum whereas violet having the least wavelength deviates the most.

Defects of vision and their correction:

Myopia (Near-sightedness) :

● A person with Myopia can see nearby objects clearly but cannot see far away objects clearly.

● It occurs due to the excessive curvature of the eye lens and elongation of the eyeball.

● The image of a distant object is formed in front of the retina and not on the retina.

● The defect is corrected by using concave lenses such that the lens will bring the image back on to the retina.

Hypermetropia (Farsightedness): ● A person with Hypermetropia can see faraway objects clearly but cannot

see nearby objects clearly. ● The near point of the eye is more than 25 cm.● This arises mostly during later stages in life, as a result of the weakening of

the ciliary muscles and/or the decreased flexibility of the lens. ● Focal length of the eye lens gets too long. ● The image of a distant object is formed behind the retina and not on the

retina.● The defect is corrected by using Convex lenses such that the lens will

bring the image back onto the retina.

Presbyopia:

● Presbyopia is a condition associated with aging of the eye that results in progressively worsening ability to focus clearly on close objects.

● It is a natural part of the aging process.

● It is due to hardening of the lens of the eye causing the eye to focus light behind rather than on the retina when looking at close objects.

● The power of accommodation of the eye usually decreases with ageing.

● The ciliary muscles weaken and thereby the flexibility of the eye lens reduces. The near point moves away.

● Spectacles with convex lenses are recommended.

Astigmatism:

● This defect is when the light rays do not all come to a single focal point on the retina, instead some focus on the retina and some focus in front of or behind it.

● This is usually caused by a non-uniform curvature of the cornea.

● Astigmatism can usually be corrected by using a special spherical cylindrical lens that is placed in the out-of-focus axis.

Capillary Action Around Us

● When we sprinkle water at the roots of trees and shrubs, the sprinkled water gradually rises to their branches upwards.

● The water rises to reach from roots to leaves in a plant via capillary action.

● When the bark of a tree (Xylem) is removed in a circular fashion all around near its base, it gradually dries up and dies because water from soil cannot rise to aerial parts.

● The rise of kerosene or oil in the wick of an oil.

● The absorption of ink in a blotting paper.

● Sandy soil gets drier earlier than clay because the interspaces between the particles of the clay form finer capillaries and water rises to the surface quickly.

● A pen nib is split at the tip to provide the narrow capillary and the ink is drawn up to the tip continuously.

● Capillary action in the human body is seen in the absorption of sweat from the skin by fabrics.

Bernoulli’s Principle

● Bernoulli's principle states that as the velocity of fluid flow increases, the pressure exerted by that fluid decreases and vice versa.

Applications of Bernoulli’s Principle

● The upper surface of wings of an aeroplane is made convex and the lower surface is made concave so that the air currents at the top have a large velocity than at the bottom.

● Therefore, the pressure above the surface of the wing is less as compared to the lower surface of the wing giving a vertical lift to the plane.

● When a strong wind blows over the roof, there is lowering of pressure on the roof.

As the pressure on the bottom side of the roof is higher, roofs are easily blown off without damaging the walls of the building.

● A suction effect is experienced by a person standing close to the platform at railway station when a fast train passes the person.

This is because the fast moving air between the person and train produces a decrease in pressure and the excess air pressure on the other side pushes the person towards the train.

● The same way that Bernoulli's principle works for creating lift in airplanes, it works for creating lift in sails of sailboats.

Thermal Expansion of Solids

● When an object is heated, its molecules vibrate and therefore need more space around them. This causes the material to expand.

Applications of Thermal Expansion of Solids:

● Blacksmiths use the principle of expansion on heating and contraction on cooling, to fix the iron rim onto the wooden wheel of a bullock cart.

● While laying railway tracks, a small gap is left between adjacent rails.

This is because the iron rails expand in summer, and the gap allows space for the expansion.

● While constructing a bridge using iron girders, one end of the girder is fixed, and some space is left at the other end, which is placed over iron rollers.

The space is left to allow the iron girder to expand during summer, and thereby prevent damage to the bridge.

● When the lid or the cork on a bottle is too tight and can’t be opened, immerse the mouth of the bottle in hot water.

The lid undergoes thermal expansion and becomes slightly loose, and then opens easily.

● Glass is a poor conductor of heat, that is, it does not allow heat to pass through it easily.

When boiling water is poured into a thick glass, the inner surface of the glass expands more rapidly than the outer surface. Due to this uneven expansion, the glass cracks.

● While constructing cement roads using concrete slabs, a small gap is left between two slabs.

The concrete slabs undergo thermal expansion during summer. The gap allows space for this expansion.

If these gaps were not left, the concrete slabs would crack during summer due to thermal expansion.

● When ships and boilers are constructed, the steel plates are joined together firmly by riveting.

A rivet is heated to red hot and passed through the plates. Then it is hammered to fix it firmly.

On cooling, the rivet contracts and holds the plates together firmly.

● In certain industries, hot liquids or hot water is transported through metal pipes from one place to another.

These pipes are subjected to expansion and contraction. To avoid cracks in the pipes when they expand and contract, they are arranged in the form of loops.

● A thermometer also works on the principle of expansion and contraction of matter on heating and cooling.

Depending on the type of material used in thermometers, they are classified into Solid, Liquid and Gas thermometers.

● Telephone and electrical cables are strung out a little loose between the poles. This is because, during winters, the wires may contract and snap.

● The pendulum of a clock made of ordinary metal expands and contracts due to variations in the temperature.

In summer, the length of the pendulum increases, and in winter, it decreases. As a result of it, an error creeps into the time shown by the clock.

To show the correct time, the pendulum is made of invar-steel, which has negligible expansion and contraction due to variations in temperature.

● In some cases, e.g. in electric bulbs, metallic wires are to be sealed into the glass.

If a copper wire is sealed through glass, the joint will crack on cooling because of unequal contraction of copper and glass.

To avoid this, platinum wire is sealed through the glass. This is because platinum and glass have almost the same rate of expansion.

Total Internal Reflection

● Total internal reflection is a phenomenon that occurs if the angle of incidence is greater than a certain limiting angle, called the critical angle.

● It takes place at the boundary between two transparent media when a ray of light passes from an optically denser medium into a rarer medium at an angle of incidence greater than the critical angle.

Applications of TIR:

Mirage:

● On hot summer days or in the deserts, patches of water appear to us, some miles in front of us, only to find none when we approach them.

● This phenomenon known as mirage is caused by total internal reflection.

● The air layers on the ground become hot and less dense in these places and light has to pass through these less-dense layers when it comes down.

● At a certain point, the light exceeds the critical angles and the total internal reflection takes place.

Reflecting Prisms:

● In optical instruments, right-angled prisms are widely used to divert the course of light rays.

● As the total internal reflection takes place within them, the loss of light energy can be kept to a minimum.

● So, the prisms are preferred to mirrors for the purpose of reflection.

Diamonds:

● The sparkles inside diamonds are cause by total internal reflection.

● Diamond is very dense and has a very large refractive index which means smaller critical angle.

● Therefore, when light enters a diamond, it is subjected to total internal reflection, that in turn causes sparkles.

Optical Fibres:

● In Optic fibres the outer layer known as cladding is less dense relative to the inner dense core - the first condition for total internal reflection.

● Since light enters almost parallel to the fibre, the angle of incidence is high and it easily exceeds the critical angle that triggers off the TIR.

Twinkling of stars

● The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation).

● Stars (except for the Sun) appear as tiny dots in the sky.

● As their light travels through thick layers of turbulent (moving) air in the Earth's atmosphere, the light of the star is bent (refracted) many times and in random directions (light is bent when it hits a change in density - like a pocket of cold air or hot air).

● This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling).

● Stars closer to the horizon appear to twinkle more than stars that are overhead.

● This is because the light of stars near the horizon has to travel through more air than the light of stars overhead and so is subject to more refraction.

● Hence, stars twinkle because they are so far from Earth that they appear as point sources of light easily disturbed by Earth's atmospheric turbulence, which acts like lenses and prisms diverting the light's path.

● Large astronomical objects closer to Earth, like the Moon and other planets, do not usually twinkle, because they are so close to us.

● They appear big enough that the twinkling is not noticeable (except when the air is extremely turbulent).

Scattering of Light● Different from reflection, where radiation is deflected in one direction,

some particles and molecules found in the atmosphere have the ability to scatter solar radiation in all directions.

● The particles/molecules which scatter light are called scatterers and can also include particulates made by human industry.

● Selective scattering (or Rayleigh scattering) occurs when certain particles are more effective at scattering a particular wavelength of light.

● Air molecules, like oxygen and nitrogen, for example, are small in size and thus more effective at scattering shorter wavelengths of light (blue and violet).

● The sky appears blue during a clear cloudless day because the molecules in the air scatter blue light from the sun more than they scatter red light.

● During sunrise and sunset, the sky appears red and orange because the blue light has been scattered out and away from the line of sight.

● Clouds are white because their water droplets or ice crystals are large enough to scatter the light of the seven wavelengths of component colours of white light (i.e VIBGYOR; red, orange, yellow, green, blue, indigo, and violet), which combine to produce white light (Mie scattering).

Rainbow Formation

● The formation of a rainbow is due to phenomena - Reflection, Refraction, Dispersion and Total internal reflection.

● They occur due to the interaction of light with air and water and the boundaries between them.

● As light enters the raindrop, it is refracted (the path of the light is bent to a different angle), and some of the light is reflected by the internal, curved, mirror-like surface of the raindrop, and finally is refracted back out the raindrop toward the observer.

Auroras● The Aurora is an incredible light show seen around the magnetic poles of

the northern and southern hemispheres. ● Auroras that occur in the northern hemisphere are called ‘Aurora Borealis’

or ‘northern lights’ and auroras that occur in the southern hemisphere are called ‘Aurora Australis’ or ‘southern lights’.

● Auroras are the result of collisions between gaseous particles (in the Earth’s atmosphere) with charged particles (released from the sun’s atmosphere).

● Variations in colour are due to the type of gas particles that are colliding. Oxygen gives off green and red light. Nitrogen glows blue and purple.

Gravitation

● Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward (or gravitate toward) one another, including objects ranging from atoms and photons to planets and stars.

● On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides.

● The gravitational attraction of the original gaseous matter present in the Universe caused it to begin coalescing, forming stars – and for the stars to group together into galaxies – so gravity is responsible for many of the large scale structures in the Universe.

● Gravity has an infinite range, although its effects become increasingly weaker on farther objects.

● Gravity is the weakest of the four fundamental forces of physics.

● As a consequence, it has no significant influence at the level of subatomic particles.

● In contrast, it is the dominant force at the macroscopic scale and is the cause of the formation, shape and trajectory (orbit) of astronomical bodies.

● For example, gravity causes the Earth and the other planets to orbit the Sun. It also causes the Moon to orbit the Earth, the formation of tides, the formation and evolution of the Solar System, stars and galaxies.

Newton's Law of Universal Gravitation:

● It states that a particle attracts every other particle in the universe with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

F= G*(m1*m2)/r^2

● Where F is the force, m1 and m2 are the masses of the objects interacting, r is the distance between the centers of the masses and G is the gravitational constant.

● Since the gravitational force is directly proportional to the mass of both interacting objects, more massive objects will attract each other with a greater gravitational force.

● In addition to depending on the amount of mass, gravity also depends on how far you are from something.

● This is why we are stuck to the surface of the Earth instead of being pulled off into the Sun, which has many more times the gravity of the Earth.

Kepler's Three Laws of Planetary Motion:

1. The Law of Ellipses

2. The Law of Equal Areas

3. The Law of Harmonies

Stars and Their Life CycleCelestial Bodies:

● By definition, a celestial body is any natural body outside the Earth’s atmosphere.

● For example Moon, Sun, and the other planets of our solar system.

● The Kuiper belt contains many celestial bodies.

● Celestial bodies can be classified into solar and extra-solar bodies and objects.

● Galaxies, stars, planets, asteroids, comets, satellites etc will fall into this classification.

Galaxies:

● A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter.

● The number of galaxies cannot be counted—the observable universe alone may contain 100 billion.

● Galaxies with less than a billion stars are considered "small galaxies."

● In our own galaxy, the sun is just one of about 100 billion stars.

● Galaxies are classified into three main types: ○ Spiral galaxies,

○ Elliptical galaxies, and

○ Irregular galaxies.

● Spiral galaxies, such as our Milky Way, consist of a flat disk with a bulging center and surrounding spiral arms.

● The galaxy's disk includes stars, planets, dust, and gas—all of which rotate around the galactic center in a regular manner.

● The Andromeda galaxy and the Large Magellanic Cloud are galaxies that can be seen with the naked eye on a clear night.

Constellations:

● A constellation is a group of visible stars that form a pattern when viewed from Earth.

● The pattern maybe that of an animal, a mythological creature, a human, or an inanimate object such as a microscope, a compass, or a crown.

● The sky was divided into 88 different constellations in 1922.

● This included 48 ancient constellations listed by the Greek astronomer Ptolemy as well as 40 new constellations.

● The 88 different constellations divide the entire night sky as seen from all around the Earth.

● The stars in each constellation may not be close to each other at all.

● Some of them are bright because they are close to Earth while others are bright because they are very large stars.

Stars:● Stars are giant spheres of superhot gas made up mostly of hydrogen and

helium. ● Stars burn hydrogen into helium in a process called nuclear fusion. This is

what makes them so hot and bright. ● Our Sun is a star.

Types of Stars: ● There are many different types of stars. Stars that are in their main sequence

(normal stars) are categorized by their color. ● The smallest stars are red and don't give off much of a glow. ● Medium size stars are yellow, like the Sun.

● The largest stars are blue and are hugely bright.

● The larger the main sequence star, the hotter and brighter they are.

Lifecycle of a Star:

Birth

● Stars start out in giant clouds of dust called nebulae. Gravity forces the dust to bunch together.

● As more and more dust bunches up, gravity gets stronger and it starts to get hot and becomes a protostar.

● Once the center gets hot enough, nuclear fusion will begin and a young star is born.

Main Sequence Star

● Once a star, it will continue to burn energy and glow for billions of years.

● The star will remain this way until it runs out of hydrogen.

● Almost 90% of the stars in the universe are main sequence stars.

● The sun is a main sequence star too. ● Towards the end of its life, a star like the Sun swells up into a red giant,

before losing its outer layers as a Planetary Nebula and finally shrinking to become a white dwarf.

Red Giant:● When the hydrogen runs out, the outside of the star expands and it becomes a

red giant.

● They have a diameter between 10 and 100 times that of the Sun and are very bright.

● But their surface temperature is lower than that of the Sun

● Very large red giants are often called Super Giants. Collapse:

● Eventually, the core of the star will start to make iron. This will cause the star to collapse.

● What happens to the star next depends on how much mass it had (how big it was). The average star will become a white Dwarf star.

● Larger stars will create a huge nuclear explosion called a Supernova.

● After the supernova, it may become a black hole or a Neutron star.

Dwarfs -

● Smaller stars are called dwarf stars.

● Red and yellow stars are generally called dwarfs.

● A brown dwarf is one that never quite got large enough for nuclear fusion to occur.

White dwarf

● It is a very small hot star at the last stage in the life cycle of a star like the Sun.

● The shrunken remains of normal stars, whose nuclear energy supplies have been used up ultimately form white dwarfs.

● They have a very high density due to gravitational effects.

● A white dwarf is the remnant of the collapse of a red giant star.Supernova

● It forms after the explosive death of a star and often gives the brightness of 100 million suns for a short time.

● The extreme burst of radiation expels the star’s material at a great velocity, driving a shock wave into the surrounding interstellar medium.

● A great proportion of primary cosmic rays comes from supernovae.

● Supernovae can form either by the sudden re-ignition of nuclear fusion in a degenerate star or by the gravitational collapse of the core of a massive star.

Neutron star

● A neutron star is created from the collapse of a giant star.

● It's very tiny but very dense.

● They are composed mainly of neutrons.

● Their mass can be three times the Sun with a diameter of only 20 km.

● If its mass is any greater, its gravity will be so strong that it will shrink further to become a black hole.

Protostar

● It appears like a star but its core is not yet hot enough for fusion.

● The phase begins when a molecular cloud first collapses under the force of self-gravity.

● It ends when the protostar blows back the infalling gas and contracts to become a main sequence star.

● Protostars are usually surrounded by dust, which blocks the light that they emit, so they are difficult to observe in the visible spectrum.

● The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly.

● Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being smaller objects, such as dwarf planets and small Solar System bodies.

● Of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury.

● The center of the Solar System is the Sun.

The Solar System

The Planets

● A planet is a large space object which revolves around a star.

● It also reflects that star's light. Eight planets have been discovered in our solar system.

● Starting with the closest to the sun they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

● The closest four planets are termed terrestrial planets, meaning they have a hard rocky surface. They are Mercury, Venus, Earth, and Mars.

● The furthest four planets -Jupiter, Saturn, Uranus, and Neptune - are called giant planets.

● Gas giants, Jupiter and Saturn, are giant planets primarily composed of hydrogen and helium and are the most massive planets in the Solar System.

● Ice giants, Uranus and Neptune, are primarily composed of low-boiling-point materials such as water, methane, and ammonia, with thick atmospheres of hydrogen and helium.

Dwarf Planets:

● Dwarf planets are objects similar to planets in the Solar System. However, they are defined as not large enough to have "cleared their orbital region of other objects."

● Some of the dwarf planets in the Solar System include Pluto, Ceres, Eris, Haumea, and Makemake.

Comets

● Comets are objects made of ice, dust, and rocks that orbit the sun.

● They often have a visible "tail" of gas that comes from solar radiation and solar wind.

● Comets originate from the Kuiper belt and the Oort cloud.

Asteroid Belt -

● The asteroid belt is a region between the planets Mars and Jupiter.

● In this region, thousands of rocky objects orbit the Sun.

● They range in size from tiny dust like particles to the dwarf planet Ceres.

Kuiper Belt

● The Kuiper belt is a region of thousands of small bodies that exist outside the orbit of the planets.

● Objects in the Kuiper belt consist of "ices" such as ammonia, water, and methane.

Oort Cloud

● The Oort cloud exists much further out than the Kuiper belt. Around a thousand times as far away from the Sun.

● Until now, scientists have only guessed the existence of the Oort cloud which they think consists of thousands of small icy objects.

● The Oort cloud is at the very edge of the Solar System.

The Sun:

● The Sun is a yellow dwarf star at the center of our Solar System.

● The Sun and the Solar System orbit around the center of our Galaxy, the Milky Way.

● The Sun is officially classified as a G-type main sequence star. It is expected to remain stable for the next 5 billion years.

● Although the Sun is a relatively small star in the universe, it is huge in relation to our solar system.

● Even with massive gas planets like Jupiter and Saturn, the Sun contains 99.8% of all the mass in the solar system.

● The Sun is made up of superheated hydrogen (about 74%) and helium gas.

Mercury:

● Now that Pluto is no longer classified as a planet, Mercury is the smallest planet in the solar system.

● Mercury has a rocky surface and an iron core.

● The iron core in Mercury is very large compared to other rocky planets like Earth and Mars.

● This makes Mercury's mass very high compared to its size.

● Mercury is a barren planet covered with craters from impacts of asteroids and other objects.

● It looks very similar to the Earth's moon and has almost the same size.

● Mercury has virtually no atmosphere and rotates very slowly in relationship to the sun.

● A single day on Mercury is as long as almost 60 Earth days.

● Since Mercury is close to the Sun, it is very difficult to send a spacecraft to explore the planet.

● The gravity from the sun will constantly pull the spacecraft causing the ship to need lots of fuel in order to stop or slow down at Mercury.

Venus:

● The entire surface of Venus is constantly covered by clouds.

● These clouds are made up mostly of carbon dioxide which has a greenhouse effect keeping in the Sun's heat like a giant blanket.

● As a result, Venus is the hottest planet in our solar system. It is even hotter than Mercury, which is much closer to the Sun.

● It is completely dry and has long rivers of molten lava and thousands of volcanoes.

● There are over 100 giant volcanoes on Venus that are each 100km or more across.

● Venus is very similar to Earth in size, mass, and gravity. It is sometimes called Earth's sister planet.

● Water, an essential part of Earth, isn't found on Venus as it all has evaporated from the heat.

● Venus actually rotates backwards (clockwise, east to west) from the way the rest of the planets rotate.

● Some scientists believe this backward rotation was caused by a giant impact with a large asteroid or comet.

Mars:

● Mars’ surface is dry and much of it is covered with a reddish dust and rocks. When viewed from Earth, Mars appears reddish.

● Olympus Mons, a now dormant volcano in Mars, is the highest mountain in the Solar System. It is 3 times as high as Mount Everest.

● Another major geographical structure of Mars is the great canyon, Valles Marineris. This canyon is the biggest in the Solar System.

● Mars often has huge dust storms with high speed winds. These dust storms are powered by the Sun and can grow to enormous proportions sending dust miles into the atmosphere and covering much of the planet.

● Unlike Earth, Mars has a very thin atmosphere made up mostly of carbon dioxide.

● As a result, it is much colder on Mars (average of -70 degrees F) than on Earth.

Jupiter:

● It is the largest planet in the Solar System; more than 300 times more massive than Earth and is more than two times as massive than all the other planets combined.

● Jupiter is called a gas giant planet. This is because its surface is made up of a thick layer of hydrogen gas.

● Jupiter's surface is very violent with massive hurricane-like storms, winds, thunder and lightning.

● The energy powering Jupiter's storms isn't from the sun but is from radiation generated by Jupiter itself.

● Jupiter is home to a number of interesting moons including Ganymede, Io, Europa, and Callisto.

● These four moons were first discovered by Galileo and are called the Galilean Moons.

● Ganymede, the largest moon in the Solar System, is larger than the planet Mercury.

Saturn:

● Saturn is the second largest planet in the solar system after Jupiter.

● Saturn is made up of mostly hydrogen with some helium.

● Overall, Saturn is the least dense planet in the solar system.

● It is the only planet that is less dense than water, meaning it would actually float on a (huge) ocean of water.

● Saturn's rings are made up of mostly ice particles with some dust and rocks as well.

● The rings are located around Saturn's equator.

● Saturn's largest moon Titan is the second largest moon in the Solar System after Jupiter's moon, Ganymede.

● Titan is the only moon in the Solar System that has a dense atmosphere.

● Titan's atmosphere is made up of mostly nitrogen.

Uranus:

● Uranus is an ice giant like its sister planet Neptune.

● As a result, Uranus has the coldest atmosphere of all the planets in the Solar System.

● The surface of Uranus is made up of mostly hydrogen gas with some helium gas as well.

● The gas atmosphere makes up about 25% of the planet.

● One of Uranus' most unique features is that it rotates on its side.

● If you picture the Sun and the planets of the solar system on a table, the other planets would rotate or spin like tops.

● Uranus, on the other hand, would roll like a marble.

● Most scientists agree that Uranus' odd rotation is because another large planetoid object collided with the planet with enough force to change its tilt.

Neptune:

● Neptune's atmosphere gives it a blue color which fits it with it being named after the Roman god of the sea.

● Neptune is an ice giant planet. This means it has a gas surface like the gas giant planets, but it has an interior composed mostly of ices and rock.

● Neptune's atmosphere is mostly made up of hydrogen with a smaller amount of helium.

● The surface of Neptune swirls with huge storms and powerful winds.

● Neptune has 14 known moons.

● The largest of Neptune's moons is Triton.

● Neptune also has a small ring system similar to Saturn, but not nearly as large nor as visible as that of Saturn.

● The largest moon, Triton, orbits Neptune backwards from the rest of the moons. This is called a retrograde orbit.

Corona● Corona is a luminous envelope of plasma that surrounds the Sun and

other celestial bodies. ● It is extended to millions of kilometres into space and is commonly seen

during a total solar eclipse. ● The intense temperature of the Sun's corona is due to the presence of highly

ionized ions which give it a spectral feature. ● The composition of the corona is the same as the interior of the Sun, mainly

made up of hydrogen but ionized form. ● The corona emits radiations that can only be observed from space and are

mainly in the form of X-rays.

Latest Development in Physics

Electromagnetic induction:

● Electromagnetic or magnetic induction is the production of an electromotive force (i.e., voltage) across an electrical conductor in a changing magnetic field.

● Electromagnetic induction has found many applications in technology, including electrical components such as inductors and transformers, and devices such as electric motors and generators.

Electromagnetic Train:

● Electromagnetic trains do not have wheels. Powerful electromagnets are attached to the bottom of the train as well as on the track.

● The north pole of the electromagnet on the track faces upwards and the north pole of the electromagnet on the train faces downwards.

● The north pole in the track repels the north pole on the train and levitates the train.

● The electric current that changes constantly allows a change in the polarity of electromagnets. This change in polarity pushes and pulls the train.

● Electromagnetic train runs faster than the ordinary train. Another significance of electromagnetic train is that it does not make a noise.

SuperconductivityComplete disappearance of electrical resistance in various solids when they are cooled below a characteristic temperature.Applications:1. The biggest application for superconductivity is in producing the

large-volume, stable, and high-intensity magnetic fields required for MRI. 2. Particle accelerators such as the Large Hadron Collider can include many

high field electromagnets requiring large quantities of low-temperature superconductors (LTS).

3. In manufacturing low-loss power cables.4. In superconducting coils to produce very strong magnetic fields.

Basics of Physics and Its Applications in Daily Life

LASER

● LASER stands for- "Light Amplification by Stimulated Emission of Radiation.”

● Laser device emits light (electromagnetic radiation) through a process called stimulated emission in which light is emitted in a narrow, low-divergence beam with the help of optical components such as lenses.

Applications of Lasers:

● Medicine as a cutting and cauterizing instrument.

● Cosmetic procedures and surgery like removing tattoos, scars, stretch marks, sunspots, wrinkles, birthmarks, and hair removal.

● LASIK eye surgery to treat myopia (nearsightedness), hyperopia (farsightedness) and astigmatism.

● In providing extremely high energy density for welding and cutting and hence are used in automobile industry.

● In the garment industry, computer controlled laser garment cutters can cut garments in just a few seconds.

● In consumer electronics, telecommunications, and data communications, lasers are used as the transmitters in optical communications over optical fibre and free space.

● Military uses of lasers include applications such as target designation and ranging, defensive countermeasures, communications and directed energy weapons.

● LIDAR technology is based on pulsed lasers. LIDAR stands for Light Detection and Ranging and is a remote sensing method.

● LIDAR technology has been in news recently as it is being used in self-driving vehicles.

RFID (Radio Frequency Identification Tag)

● Radio-Frequency Identification is the use of radio waves to read, capture, and interact with information stored on a tag.

● Tags are usually attached to objects and can be read from several feet away.

● Furthermore, the tag doesn’t always have to be in the direct line-of-sight to initiate interaction.

Applications of RFID:

1. Goods management and tracking

2. Person and animal tracking

3. Contactless payments

4. Travel documents

5. Barcodes and security tags

6. Healthcare data management

3D Printing● 3D printing refers to processes in which material is joined under

computer control to create a three-dimensional object.

● Objects can be of almost any shape or geometry and typically are produced using digital model data from a 3D model.

● The term "3D printing" originally referred to a process that deposits a binder material onto a powder bed with inkjet printer heads layer by layer.

● It is also known as “additive manufacturing” (AM).

● In the current scenario, 3D printing or AM has been used in manufacturing, medical, industries and sociocultural sectors.

Quantum Mechanics/Physics

● Quantum mechanics is the science dealing with the behaviour of matter and light on the atomic and subatomic scale.

● It deals with electrons, protons, neutrons, and other more esoteric particles such as quarks and gluons.

● It tries to analyse properties like interactions of the particles with one another and with electromagnetic radiation (i.e., light, X-rays, and gamma rays).

LIGO and Gravitational Waves

● When an object accelerates, it creates ripples in space-time, just like a boat causes ripples in a pond. These space-time ripples are gravitational waves.

● These waves travel across the universe at the speed of light.

● They were predicted to exist by Albert Einstein in 1916 as a consequence of his General Theory of Relativity.

● Scientists have been trying to detect them using two large laser instruments in the United States, known together as the Laser Interferometer Gravitational-Wave Observatory (LIGO), as well as another in Italy.

● Discovery of gravitational waves represent a scientific landmark, opening the door to an entirely new way to observe the cosmos.

● It will unlock secrets about the early universe and mysterious objects like black holes and neutron stars.

● IndIGO, the Indian Initiative in Gravitational-wave Observations, is an initiative to set up advanced experimental facilities, for a multi-institutional Indian national project in gravitational-wave astronomy, located at Aundha, Hingoli, Maharashtra.

● A new gravitational wave detector to measure ripples in the fabric of space and time is set to be built in India by 2025, in collaboration with universities from across the globe.

Neutrino and INO Project● Neutrinos are tiny particles that travel at near light speeds.

● They generate from events like exploding stars, nuclear fusion in the sun and gamma ray bursts.

● Neutrinos are abundant in the universe, can move easily through matter and are very difficult to track down.

● The INO project primarily aims to study atmospheric neutrinos in a deep cavern in the Bodi West Hills in Theni district, Tamil Nadu.

● If completed, it would house the largest magnet in the world.

● Nicknamed the ‘blueprint of nature’, neutrinos can help scientists understand some of the most fundamental questions in physics — such as

○ understanding the evolution of the universe,

○ figuring out the energy production mechanism in the Sun and

○ why the universe is made up of matter, not antimatter.

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