General Knowledge & General Awareness Notes: General Science - Physics

GENERAL SCIENCE - PHYSICS

PHYSICAL QUANTITIES

- Physical quantities may be divided in two classes: 1. Scalar Quantities 2. Vector Quantities
- A scalar quantity is one which has only magnitude.
- A vector quantity has both magnitude and direction.
- Force, Velocity, Momentum, Acceleration are examples of vector quantities.
- Mass, length, time, volume, speed, energy, work are examples of scalar quantities.

UNITS
- All measurements in physics require standard units.
- In 1960, the General Conference of Weights and Measures recommended that a metric system of measurements called the International System of Units, abbreviated as SI units, be used.

Some Important Units
S.No. - Units - Quantity

1. Metre Length
2. Kilogram Mass
3. Second Time
4. Ampere Electric Current
5. Candela Luminous Intensity
6. Newton Force
7. Joule Workdone
8. Watt Power
9. Coulomb Electric Charge
10. Volt Potential Difference
11. Ohm Electrical Resistance
12. Farad Capacitance
13. Henry Inductance
14. Lumen Luminous Flux
- Very small distances are measured in micro-meters or (microns) (μm), angstroms (Å), nanometers (nm) and femtometres (fm).

MOTION
- When a body changes its position with respect to something else as time goes on, we say the body is in motion.
- There are two types of motion—translational (linear) and rotational (spin).
- The motion of a car on a road is translational whereas the motion of a top, spinning on its axis is rotational.

SPEED
- It is a scalar form of velocity and is defined as the distance travelled in one second.
- Speed = distance travelled time required
- SI unit of speed is m/s.

VELOCITY
- The distance covered by an object in a specified direction in unit time interval is called velocity.
- The SI unit of velocity is m/s.
- Velocity is a vector quantity.

ACCELERATION
- The velocity of a body changes due to change in its speed or direction or both. The rate of change of the velocity of a body is called its acceleration.
- Acceleration = change in velocity time taken

FORCE AND MOTION

GRAVITATIONAL FORCE
- It is the force of attraction between two masses.
- It is gravitational force that holds the moon in its orbit round the earth and the earth in its orbit round the sun.
- Newton's Law of Universal Gravitation states that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
- The value of G is 6.67 × 10–11 SI units.

CENTRIPETAL FORCE
- The force acting towards the centre on a particle executing uniform circular motion is called centripetal force and is given by 38 mv^2 r , F  where, m = Mass of the object v = Speed r = Radius of the Circular Path
- In case of the moon, gravitational force between the earth and the moon acts as the centripetal force.
- Centripetal force always acts on the particle performing circular motion.

CENTRIFUGAL FORCE
- The pseudo force that balances the centripetal force in uniform circular motion is called centrifugal force.
- Centrifugal force is directed away from the centre along the radius.
- The centrifugal force is zero exactly at the poles and maximum at the equator.

WEIGHT
- The weight of a body is the force with which the earth attracts the body towards its centre.
- The mass of a body is a constant quantity whereas its weight varies slightly from place-to-place on the earth.
- The weight of a body is maximum at the poles and minimum at the equator. This variation in weight is due to:
1. the shape of the earth.
2. the rotation of the earth about its axis.
- The weight of an object is less at high elevations than at sea level.
- At the centre of the earth, the weight of a body would be zero.
- On the surface of the moon the value of the acceleration due to gravity is nearly one-sixth of that on earth and, therefore, an object on the moon would weigh only onesixth its weight on the earth. The mass of an object on the moon would be the same as on earth.
- The weight of a body would be more if the earth stopped rotating. Conversely, if the speed of rotation were higher, the weight would be less.
- A person weighs more in a lift, which is accelerating upward.
- An astronaut feels weightless in a spaceship because he is not pushing against anything.

FRICTION
- Friction is the force which opposes the relative motion of two surfaces in contact.
- It is friction between the ground and the soles of our shoes that makes walking possible and it is lack of friction that makes our feet slip on highly polished surfaces.
- Friction in machines wastes energy and also causes wear and tear. This friction is reduced by using (1) lubricants, and (2) ball bearings.

NEWTON'S LAWS OF MOTION
First Law
- Every object continues in its state of rest or of uniform motion in a straight line if no net force acts upon it. It is also known as law of inertia.
- Examples: 1. An unwary passenger in a fast-moving bus falls forward when it stops suddenly. This happens because the feet of the passenger come to rest suddenly whereas his upper part of body continues to be in motion. 2. A person getting down from a moving bus has to run some distance, in the direction of the bus, before stopping. If he does not run he is bound to fall because his feet come to rest whereas his body continues to be in motion.

Momentum
- The momentum of a body is defined as the product of its mass and velocity.

Newtons' Second Law
- This law states that 'the rate of change of momentum of a body is proportional to the applied force and takes place in the direction of the force.'
- If we express force (F) in Newtons, mass (m) in kilograms and acceleration (a) in metres per second squared, we can write the second law as; F = ma.
- In travelling the same distance, a car consumes more fuel on a crowded road than on a free road. This happens because the car has to stop and start quite often on a crowded road. The repeated acceleration requires a force (second law), which ultimately comes from the fuel. On a free road the car runs at almost uniform speed requiring fewer accelerations and hence less fuel consumption.

Newton's Third Law
- This law states that 'to every action there is an equal and opposite reaction.'
- When a bullet is fired from a gun, equal and opposite forces are exerted on the bullet and the gun.
- The engine in a jet aeroplane works on the same principle as a rocket but there is a difference in the method of obtaining the high velocity as jet.

IMPULSE
- If a force acts on a body for a very short time, then the product of force and time is called the impulse.
Impulse= Change in momentum

Application of Impulse
1. A cricket player draws his hand back while catching.
2. A person jumping on hard cement floor receives more injuries than a person jumping on muddy or sandy floor.

WORK, POWER AND ENERGY

WORK
- Whenever a force acting on a body displaces it, work is said to be done.

Work = Force × Distance moved in the direction of force.
- Work is a scalar quantity and its SI unit is Joule (J).\

POWER
- Power is defined as the rate of doing work.

Work done
Power =
Time taken
- The SI unit of power is Watt (W) and is also measured in horse power.

1 HP = 746 W

ENERGY
- Energy is defined as the capacity to do work.

Kinetic Energy
- The energy possessed by an object due to its motion is called kinetic energy and is described by the expression

KE = 1/2 mv^2 ; where, m = mass of the object v = speed

Potential Energy
- Potential energy is the energy possessed by the body by virtue of its position, configuration or any condition of stress or strain.
- There are many examples of potential energy. A stone held at some height above the ground has potential energy. Water in an elevated reservoir possesses potential energy.

Transformation of Energy
S.No. - Equipment Transformation

1. Dynamo Mechanical energy into electrical energy
2. Microphone Sound energy into electrical energy
3. Loud Speaker Electrical energy into sound energy
4. Electric Bulb Electrical energy into light and heat energy
5. Battery Chemical energy into electrical energy
6. Electrical Motor Electrical energy into mechanical energy

CENTRE OF GRAVITY
- The centre of gravity of a body is the point where the whole weight of the body can be considered to act.
- Racing cars are build low and with wide wheel bases to reduce the risk of overturning at sharp bends.
- While crossing a river in a boat, passengers are not allowed to stand. This keeps the CG of the system (boat and passengers) low and ensures stability.

ARTIFICIAL SATELLITES
- In the case of a satellite, the centripetal force is provided by the gravitational pull of the earth.
- If the speed of a satellite is more than 11.2 km/s or 25,000 miles/hour, the satellite would escape the earth entirely and would never come back. This is called escape velocity.
- The existence of gaseous atmosphere on the earth is due to the high value of its escape velocity.

Geostationary Satellites
- Geostationary satellites are stationary with respect to an observer on the earth. Their time period is 24-hour. There height above the surface of earth is 36,000 km. They are always in equatorial plane and their orbits are circular.
They are also called parking orbits.

DENSITY AND RELATIVE DENSITY

DENSITY
- The mass per unit volume of a substance is called its density.
Density = Mass / Volume

- The SI unit of density is kilogram per metre cubed (kg/m3).
- The relative density of a substance is the ratio of the density of the substance to the density of water.
- Relative density has no unit.

PRESSURE
- Pressure is defined as force acting per unit area.

Pressure = Force / Area

- The SI unit of pressure is newton per metre squared or pascal.
- Broad wooden sleepers are placed below the rails to reduce the pressure exerted by the weight of a train.
- The pressure of water increases with depth, therefore bottom of a dam is made much thicken than the top.
- The pressure exerted on an enclosed liquid at one place is transmitted equally throughout the liquid. This is called Pascal's Principle.
- Hydraulic presses, hydraulic brakes, hydraulic door closers, etc. are applications of the Pascal's Principle.
- At high attitudes where atmosphere pressure is less nose bleeding may occur due to the greater pressure of blood.
- In an aircraft flying at high altitude, normal atmospheric pressure is maintained by the use of air pumps. If this were not done, the crew and passengers would experience difficulty in breathing and consequently face dangers.
- Atmospheric pressure is measured with an instrument called the Barometer.

ARCHIMEDE'S PRINCIPLE
- This principle states that when a body is wholly or partially immersed in a fluid, it experiences an upthrust (upward force) equal to the weight of the fluid displaced.
- An iron nail sinks in water whereas a ship made of iron and steel floats. This is due to the fact that a ship is hollow and contains air and, therefore, its density is less than that of water.
- The density of sea water is more than that of river water, due to this a ship sinks less in sea water. It is for this reason that a ship rises a little when it enters a sea from a river.
- It is because of the higher density of sea water that it is easier to swim in the sea.
- A balloon filled with a light gas, such as hydrogen, rises because the average density of the balloon and the gas is less than that of air. The balloon cannot rise indefinitely because the density of the air decreases with increasing altitude. At a certain height, where the density of air is equal to the average density of the balloon, it ceases to rise and drifts sideways with the wind.
- When an ice block floats in water the water level will remain the same when all the ice melts into water.
- A hydrometer is an instrument used for measuring the relative density of liquids.
- A special type of a hydrometer called Lactometer is used for testing milk by measuring its density.

SURFACE TENSION
- Surface tension is that property of liquids owing to which they tend to acquire minimum surface area.
- Surface tension is caused by molecular attractions.
- When a paint brush is dipped in water all its hair spread out but when it is taken out it is covered with a thin film of water which contracts due to surface tension and pulls the hair together.
- Liquid drops, such as raindrops, oildrops, drops of molten metals, dewdrops etc. are all spherical because their surface tend to contract in order to have minimum surface area.

For a given volume, a sphere has the minimum surface area.
- Soaps and detergents lower the surface tension of water.

This increases the wetting power of water or its ability to detach dirt particles from clothes and untensils.
- The force of attraction between unlike molecules is called adhesion and that between like molecules cohesion.
- The melted wax of a candle is drawn up into the wick by capillary action. Oil rises up a lamp wick for the same reason.
- If one end of a sugar cube is dipped into tea, the entire cube is quickly wet on account of capillary action.

VISCOSITY
- The force which opposes the relative motion between different layers of liquid or gases is called viscous force.
- Viscosity is the property of liquids and gases both.

BERNOULLI'S THEOREM
- According to Bernoulli's theorem, in case of streamline flow of incompressible and non-viscous fluid (ideal fluid) through a tube, total energy (sum of pressure energy, potential energy and kinetic energy) per unit volume of fluid is same at all points.
1. When a bowler spins a ball, it changes its direction (swings) in the air due to unequal pressure acting on it.

HEAT
- Heat is that form of energy which flows from one body to other body due to difference in temperature between the bodies. The amount of heat contained in a body depends upon the mass of the body.

TEMPERATURE
- The temperature of a body is the quantity that tells how hot or cold it is with respect to some standard body.

MEASUREMENT OF TEMPERATURE
- Temperature is measured by a thermometer.
- A thermometer may be graduated in following scales—

1. The upper and lower points of centigrade scale are 100°C and 0°C.
2. The upper and lower points of Fahrenheit scale are 212°F and 32°F.
3. The upper and lower points of Reaumur scale are 80°R and 0°R.
4. The upper and lower points of Kelvin scale are 373K and 273K.
5. The upper and lower points of Rankine scale are 672°Ra and 460° Ra.
- At –40 degrees both celsius and Fahrenheit scales will show identical readings.
- Water cannot be used in a thermometer becaues it freezes at 0°C and also because of its irregular expansion.

THERMAL EXPANSION
- Solids, liquids and gases generally expand when heated and contract when cooled.
- Gaps have to be left in railway tracks to make allowance for expansion, otherwise the rails will buckle. Allowance is made for the expansion of long steel bridges. One end of such bridge is fixed while the other rests on rollers.
- Telephone wires sag more in summer than in winter due to thermal expansion.

EXPANSION OF WATER
- Water has its minimum volume and maximum density at 4°C.

TRANSMISSION OF HEAT
- There are three way s of heat transmission:

1. Conduction; 2. Convection; 3. Radiation.

Conduction
- In this process, heat is transferred from one place to other place by the successive vibration of the particles of the medium without bodily movement of the particles of the medium.
- Conduction takes place mainly in solids.
- Air is a very bad conductor of heat. The good insulating properties of wool, cotton, etc. are mainly due to the air spaces they contain.

Convection
- In this process, heat is transferred by the actual movement of particles of the medium from one place to other place.
- In liquids and gases heat is transmitted by convection.

Radiation
- In this mode of heat transmission heat is transferred from one place to another without effecting the intervening medium.

HEAT CAPACITY
- The heat capacity of a body is defined as the heat required to raise the temperature of the body by 1K. Its SI unit is J/K.

SPECIFIC HEAT CAPACITY
- The specific heat capacity of a substance is the heat required to raise the temperature of a unit mass of the substance by 1K.
- Its SI unit is J/kg K.
- It is because of its high specific heat capacity that water is used as a cooling liquid in car engine.

LATENT HEAT
- It is defined as the amount of heat absorbed or given out by a body during the change of state.
- Each gram of ice that melts absorbs 336 J of heat.

EVAPORATION
- Water can change into the vapour state either by boiling or by evaporation at lower temperatures.
- When sweat evaporates from the skin it draws much heat from the body and produces a cooling sensation.
- In summer, water is stored in pitchers for cooling. Water oozes out of the pores of the pitchers and cools on evaporation.
- The rate of evaporation increases with increase in temperature.

REFRIGERATOR
- In a refrigerator, cooling is produced by the evaporation of a volatile liquid, freon, inside a copper coil (evaporator), which surrounds the freezer.
- The cooling unit (freezer) in a refrigerator is fitted near the top to cool the whole of the interior.

RELATIVE HUMIDITY
- Relative humidity is defined as the ratio of the mass of water vapour in a given volume of air to the mass required for saturating the same volume of air at the same temperature.
- Relative humidity is measured with an instrument called the hygrometer.

PRESSURE COOKER
- The boiling point of a liquid depends on external pressure.
- When the atmospheric pressure is 76 cm of mercury, water boils at 100°C. But when the pressure is increased, the boiling point of water is raised.
- In a pressure cooker, water boils at temperatures higher than 100°C due to increased pressure. The increased boiling temperature allows water to hold more heat which cooks food faster.
- At higher altitudes, atmospheric pressure is reduced. This lowers the boiling point of water and food takes much longer to cook.

WAVE MOTION
- Wave motion may be defined as the transfer of energy without the net transfer of matter.
- If the particles of the medium vibrate perpendicular to the direction of propagation of wave, the wave is called transverse wave.
- Light waves are transverse waves.
- If the particles of the medium vibrate in the direction of propagation of wave, the wave is called longitudinal wave.
- Sound waves are longitudinal waves.

ELECTROMAGNETIC WAVE
- Electromagnetic waves include an enormous range of frequencies—from radio waves with frequencies less than 105 Hz to gamma rays having frequencies greater than 1020 Hz.
- All electromagnetic wave have the same speed (3 × 108 m/s) in vacuum. The relation v = n- holds good for all electromagnetic waves.

RADIO AND TELEVISION TRANSMISSION
- Radio waves sent out by radio stations are reflected by the ionosphere and can be received anywhere on the earth.
- At night the radio reception improves because the layers of the ionosphere are not exposed to sunlight and are more settled.
- Radar (Radio detection and ranging) employs high frequency radio waves for detecting objects like ships and aeroplanes.
- In microwave oven, when the waves fall on the food, these are absorbed by water, fats, sugars and certain other molecules whose consequent vibrations produce heat.
Since heating occurs inside the food, without warming the surrounding air, the cooking time is greatly reduced.
- In microwave oven, food cannot be cooked in metal vessels because the metal blocks out the microwaves.

LIGHT
- Light is a form of energy which is propagated as electromagnetic waves.
- Light is a transverse wave.
- Speed of light in vacuum is 3 × 108 m/s.
- Light takes 8 minute 16.6 second to reach from sun to earth.

REFLECTION
- When light is incident upon a surface, part of it is reflected.
But certain surfaces like mirrors and polished metals reflect almost all the light incident upon them.
- The law of reflection states that the angle of incidence is equal to the angle of reflection.
- To see full image in a plane mirror, a person requires a mirror of at least half of his height.

INCLINED MIRROR (NO. OF IMAGES)
- When an object is placed between two inclined mirrors, several images of the object are formed.

CURVED MIRRORS
- There are two types of curved spherical mirrors—1. Concave Mirror, 2. Convex Mirror.
- Concave mirror can concentrate the sun's radiation falling on it at one point, it can be used as a burning glass.
- Concave mirrors are also used in solar cookers.
- Large concave mirrors are used in reflecting telescopes for observing and photographing distant stars and other heavenly bodies.
- Concave mirror is also used as a shaving or make-up mirror.
- Small concave mirrors are used by dentists for examining teeth.
- Concave parabolic mirrors are used in searchlight and headlamps of cars.
- Convex mirrors are also used as rear view mirrors in vehicles.

REFRACTION
- When a ray of light passes from one medium to other it suffers a change in direction at the boundary of separation of two media. This phenomenon is called refraction.
- When a ray passes from one medium to another optically denser medium, e.g., from air to water or glass, it bends towards the normal. Conversely, a ray passing from water or glass into air is bent away from the normal.
- Rivers appear shallow, coin in a beaker filled with water appears raised, due to refraction.
- Another effect of refraction is the apparent upward bending of the immersed portion of a stick when dipped in water.
- It is due to refraction, produced by the earth's atmosphere, that the sun is visible for several minutes after it has set below the horizon. Thus, atmospheric refraction tends to lengthen the day.
- When the sun (or moon) is near the horizon, it appears elliptical, i.e., with the vertical diameter less than the horizontal diameter. This happens because rays from the lower edge of the sun are bent more than those from the upper edge (Atmospheric Refraction).
- One of the most interesting effects of atmospheric refraction and Mirage is a combined effect of atmospheric refraction and total internal reflection.

DISPERSION
- White light consists of seven colours—violet, indigo, blue, green, yellow, orange and red. These colours are called the spectrum of the white light.
- Violet has the minimum wavelength (or maximum frequency) and red the maximum wavelength (or minimum frequency).
- Due to different speeds, the colours are refracted through different angles and therefore, when a narrow beam of white light passes through a glass prism, it is split up into its constituent colours. This separation of light into colours is called dispersion.

COLOUR OF OBJECTS
- We see objects because of the light they reflect.
- When a rose is viewed in white light, its petals appear red and the leaves appear green, because the petals reflect the red part of the white light and leaves reflect the green part. The remaining colours are absorbed. When the same rose is viewed in green light, the petals will appear black and the leaves green. In blue or yellow light both the petals and leaves will appear black.
- Red, blue and green are primary colours.

LENSES
- There are mainly two types of lenses:
1. Convex or Converging Lens
2. Concave or Diverging Lens
- Converging or convex lens is used as a magnifying glass.
- Power of a lens is its capacity to deviate a ray. Power of a lens is measured as the reciprocal of the focal length.
P = f1 (where P is the power in diopters and f is the focal length in metres.)
- SI unit of power of lens is dioptre (D).
- The power of a converging lens is positive and that of a diverging lens is negative.
- For all positions of the object, the images formed by diverging (concave) lens are virtual, erect and diminished.

EYE
- The light entering the eye is focused by the eye-lens to form an image on the retina.
- In front of the eye, lens is the coloured part of eye, called the iris, which automatically adjusts the size of the pupil to the intensity of light falling on it.
- In bright light the iris automatically shuts tighter, reducing the amount of light entering the pupil. This protects the retina from getting damaged.
- When a person enters a dark room after being in bright light, he is not able to see clearly for a while because the iris is unable to dilate the pupil immediately.
- Least distance of distinct vision is 25 cm.

DEFECTS OF VISION
- A person suffering from long sight (hyper-metropia) can clearly see objects at infinity but cannot see near objects clearly. This defect is caused by the eyeball being too short and can be corrected by wearing converging lenses.
- In the case of a person suffering from short sight (myopia), the eye ball is too long and distant objects are focused in front of the retina. This defect can be corrected by wearing diverging lenses.
- Astigmatism: Curvature of cornea becomes irregular and image is not clear. Cylindrical lens is used.

SCATTERING OF LIGHT
- When light falls on atoms and molecules, it is scattered in all directions.
- Scattering of light is maximum for violet colour and minimum for red colour.
- Blue colour of sky is due to scattering of light.
- In the evening, the sun is lower in the sky and its light has to traverse a longer path through the atmosphere to reach an observer. Thus, at sunset, blue, green and other colours having been scattered only red and some orange light reach us and the sun appears a deep orange-red.
- In outerspace, i.e., beyond the atmosphere, there is nothing to scatter the sunlight and therefore the sky appears dark and stars are visible even in the presence of the sun.

INTERFERENCE OF LIGHT
- The superposition of two (or more) waves of the same kind that pass the same point in space at the same time is called interference.
- Beautiful colours seen in soap bubbles and oil films on water are produced due to the interference of white light reflected by these surfaces.
- LASER (Light Amplification by Stimulated Emission of Radiation) is an optical device which produces an intense beam of coherent monochromatic light.
- Examples of Interference of Light: Holography, Laser.

DIFFRACTION OF LIGHT
- When a beam of light passes through a narrow slit or an aperture, it spreads out to a certain extent into the region of geometrical shadow. This is an example of diffraction, i.e., of the failure of light to travel in a straight line.

SOUND
- Sound waves are longitudinal and cannot travel in vacuum. The transmission of sound requires a medium : air, liquid or solid.
- The longitudinal mechanical waves which lie in the frequency range 20 Hz to 20,000 Hz are called audible or sound waves. These waves are sensitive to human ear.
- The longitudinal mechanical waves having frequencies less than 20 Hz are called Infrasonic. These waves are produced by sources of bigger size such as earthquakes, volcanic eruptions, ocean waves etc.
- The longitudinal waves having frequencies greater than 20,000 Hz are called ultrasonic waves. Human ear cannot detect these waves. But some animals such as cats, dogs, bats can detect these waves.

PITCH
- The pitch (shrillness of a sound) depends on its frequency.
- A sound of higher frequency has a higher pitch.
- The pitch of a woman's voice is higher than that of a man.

LOUDNESS
- The relative loudness of a sound is measured in decibels (db).
- All stringed instruments, such as the violin, sitar, guitar, etc. have sound boxes attached to increase the loudness.

SPEED OF SOUND
- The presence of water vapour in the air increases the speed of sound.
- Sound travels faster through warm air than through cold air. The speed of sound is higher on a hot day than on a cold day.
- Thunder is heard much after the flash of lightning is seen because of the wide difference in the speeds of light and sound.

REFLECTION OF SOUND
- When a sound wave is reflected by a distant obstacle, such as a wall or a cliff, an echo is heard.
- To hear echo, the minimum distance between the observer and reflector should be 17 m.
- Exploration of underwater gas and oil is done by detecting the echoes of shock waves produced by explosions on the water surface.
- Bats emit ultrasonic waves of frequencies up to 80,000
Hz and use the reflection of these waves (echoes) to determine the presence and distance of objects on their way and from them respectively.

DOPPLER EFFECT
- The Doppler effect is the change in frequency of a wave (sound or light) due to the motion of the source or observer.
- It is due to the Doppler effect that the whistle of a train appears shriller when it approaches a listener than when it moves away from him.

ELECTRICITY
- Electricity produced by friction between two dissimilar objects is known as static electricity. Depending on the nature of the objects, one acquires a positive charge and the other an equal negative charge. For example, if a glass rod is rubbed with silk, the rod acquires positive charge and the silk an equal negative charge.
- Lightning is a gigantic electric discharge occurring between two charged clouds or between a charged cloud and the earth.

CONDUCTOR
- Conductors are those materials which allow electricity (charge) to pass through themselves.
- Metals conduct electricity because they have a large number of conduction or free electrons.

INSULATORS
- Insulators are those materials which do not allow electricity to flow through themselves. Insulators have no free electrons.

SUPER CONDUCTORS
- The resistance of metals to flow of electricity reduces with decreasing temperature. At temperatures near absolute zero, metals have almost zero resistance and became super conductors.

SEMI-CONDUCTORS
- Certain materials, such as silicon and germanium, have electrical resistivity intermediate between those of conductors and insulators. These materials are termed as semi-conductors.
- Semi-conductors are good insulators in their pure crystalline form but their conductivity increases when small amounts of impurities are added to them.

ELECTRIC CURRENT
- Electric current is simply the flow of electric charge. In solid conductors the flow of electrons and in fluids the flow of ions as well as electrons constitute the current.
- SI units of electric current is Ampere (A).

ELECTRICAL RESISTANCE
- When electric current flows through a conductor, e.g., a metallic wire, it offers some obstruction to the current.
This obstruction offered by the wire is called its electrical resistance.
- SI unit of Resistance is ohm.

OHM'S LAW
- If physical conditions like temperature, intensity of light etc. remains unchanged then electric current flowing through a conductor is directly proportional to the potential difference across its ends.

ELECTRIC MOTOR
- In an electric motor, electrical energy is converted into mechanical energy.
- Electric fans, mixers, washing machines, etc. work on electric motors.

INVERTER
- An inverter is a device which converts DC to AC. The inverters used in homes and offices are specially designed to:
1. Convert DC from a battery to AC, and
2. Charge the battery.

FUSE
- Electric fuse is a protective device used in series with an electric appliance to save it from being damaged due to high current.
- A fuse is a short piece of wire made of a tin-lead alloy, which has a low melting point.
- Fuses are always connected in the live wire in series.

COST OF ELECTRICITY
- The consumption of electrical energy in a house is measured in the unit kWh.
- Kilowatt hour is equal to the energy consumed in the circuit at the rate of 1 kilowatt for 1 hour.

MAGNETISM
- A magnet attracts and holds pieces of iron but does not attract pieces of copper.
- Iron, cobalt, nickel and certain alloys are strongly magnetic whereas copper, wood, glass, etc. are non-magnetic.
- Our earth behaves as a powerful magnet whose south pole is near the geographical north pole and whose north pole is near the geographical south pole.

ATOMIC & NUCLEAR PHYSICS
- Atom consists of three fundamental particles electron, proton and neutron. All the protons and neutrons are present in the central core of atom called nucleus. Electrons revolve around the nucleus.
- The total number of protons in the nucleus is called atomic number (Z).
- The total number of proton and neutrons in the nucleus is called mass number (A).
- Ernest Rutherford, discovered nucleus by the scattering of -particles from gold foil.

RADIOACTIVITY
- Henry Bacquerel (1896) observed that a photographic plate blackened, when placed near double sulphate of potassium and uranium. He further observed that uranium emitted special kind of rays. They were called Becqueral rays.
- Pierre and Marie Curie observed that the radiation from pitchblende was four times stronger than uranium. In 1898, they finally discovered two new substances—Polonium and Radium. These newly discovered substances were called radioactive substances and this property of these substances was named radioactivity.
- No radioactive substance emits both  and  particles simultaneously.

X-RAYS
- X-rays are electromagnetic radiations having wavelength from a fraction of an Angestrom to about 100Å. They were discovered by Rontgen during his studies on the electrical discharge phenomena in gases—he found that an unknown radiation was produced when electrons collided with the walls of the tubes.

ATOMIC ENERGY
- India today ranks sixth in the atomic energy programmes. It has developed the required know-how and expertise to manufacture nuclear weapons, but it believes in the peaceful uses of atomic power. The Atomic Energy
Commission was set-up in the country in 1948 under the Chairmanship of Dr. H. J. Bhabha.
- Bhabha Atomic Research Centre (BARC): The Bhabha Atomic Research Centre at Trombay near Mumbai (Maharashtra) has four research reactors: (i) APSARA—<br>I. is the first atomic reactor in Asia; (ii) CIRUS—It is a joint Indo-Canadian project; (iii) PURNIMA II—a zero energy fast reactor, and (iv) DHRUVA—a high power completely indigenous nuclear research reactor with most advanced laboratories in the world. Another fast breeder reactor KAMINI at Kalpakkam has been constructed.
Today India is the seventh country in the world and the first developing nation to have mastered the fast breeder reactor technology.
- Nuclear Power: Under Nuclear Power Corporation of India Limited (NPCIL) there are seven nuclear power stations in operation in six States: (i) Tarapur—Maharashtra, (ii) Rawatbhata —Rajasthan, (iii) Kalpakkam—Tam il Nadu, (iv) Narora—U.P., (v) Kakrapara—Gujarat, (vi) Kaiga—Karnataka and (vii) Kudankulam—Tamil Nadu.
- Heavy Water: Heavy water is one of the essential input for Pressurised Heavy Water Reactors (PHWRs) used both as a coolant and moderator. The first heavy water plant was set-up in 1962 in Nangal. Subsequently 7 more plants have been set-up at (i) Baroda, (ii) Tuticorin, (iii) Kota, (iv) Talcher, (v) Thal, (vi) Hazira and (vii) Manuguru.
- Research and Development Centres: Four research centres namely (i) Bhabha Atomic Research Centre, Trombay (Maharashtra), (ii) Indira Gandhi Centre for Atomic Research, Kalpakkam (Tamil Nadu), (iii) Centre for Advanced Technology, Indore (Madhya Pradesh), (iv) Variable Energy Cyclotron Centre at Kolkata (West Bengal) are focal points of research and development work in nuclear energy and related discipline.
- India's Nuclear Explosions: On May 18, 1974 India conducted her first underground nuclear explosion at Pokhran (Rajasthan) in the Thar desert, 20 km. away from Jaisalmer, at a depth of more than 100 metres. The successful explosion made India the sixth nuclear nation in the world.
- India conducted 5 nuclear explosion tests at Pokhran in two phases on May 11 and May 13, 1998 and became a nuclear power state.

IMPORTANT INVENTIONS
Name of Invention - Inventor - Nationality - Year

Aeroplane Orville & Wilbur Wright U.S. A. 1903
Ball-Point Pen John J. Loud U.S. A. 1888
Barometer Evangelista Torricelli Italy 1644
Bicycle Kirkpatrick Macmillan Britain 1839-40
Bifocal Lens Benjamin Franklin U.S. A. 1780
Car (Petrol) Karl Benz Germany 1888
Celluloid Alexander Parkes Britain 1861
Cinema Nicolas & Jean Lumiere France 1895
Clock (mechanical) I-Hsing & Liang Ling-Tsan China 1725
Diesel Engine Rudolf Diesel Germany 1895
Dynamo Hypolite Pixii France 1832
Electric Lamp Thomas Alva Edison U.S. A. 1879
Electric Motor (DC) Zenobe Gramme Belgium 1873
Electric Motor (AC) Nikola Tesla U.S. A. 1888
Electro-magnet William Sturgeon Britain 1824
Electronic Computer Dr. Alan M. Turing Britain 1943
Film (moving outlines) Louis Prince France 1885
Film (musical sound) Dr. Le de Forest U.S. A. 1923
Fountain Pen Lewis E. Waterman U.S. A. 1884
Gramophone Thomas Alva Edison U.S. A. 1878
Helicopter Etienne Oehmichen France 1924
Jet Engine Sir Frank Whittle Britain 1937
Laser Charles H. Townes U.S. A. 1960
Lift (Mechanical) Elisha G. Otis U.S. A. 1852
Locomotive Richard Trevithick Britain 1804
Machine Gun James Puckle Britain 1718
Microphone Alexander Graham Bell U.S. A. 1876
Microscope Z. Janssen Netherlands 1590
Motor Cycle G. Daimler Germany 1885
Photography (on film) John Carbutt U.S. A. 1888
Printing Press Johann Gutenberg Germany c.1455
Razor (safety) King C. Gillette U.S. A. 1895
Refrigerator James Harrison & Alexander Catlin U.S. A. 1850
Safety Pin Walter Hunt U.S. A. 1849
Sewing machine Barthelemy Thimmonnier France 1829
Ship (steam) J.C. Perier France 1775
Ship (turbine) Hon. Sir C. Parsons Britain 1894
Skyscraper W. Le Baron Jenny U.S. A. 1882
Slide Rule William Oughtred Britain 1621
Steam Engine (condenser) James Watt Britain 1765
Steel Production Henry Bessemer Britain 1855
Steel (stainless) Harry Brearley Britain 1913
Submarine David Bushnell U.S. A. 1776
Tank Sir Ernest Swinton Britain 1914
Telegraph M. Lammond France 1787
Telegraph Code Samuel F.B. Morse U.S. A. 1837
Telephone (perfected) Alexander Graham Bell U.S. A. 1876
Television (mechanical) John Logie Baird Britain 1926
Television (electronic) P.T. Farnsworth U.S. A. 1927
Thermometer Galileo Galilei Italy 1593
Transformer Michael Faraday Britain 1831
Transistor Bardeen, Shockley & Brattain U.S. A. 1948
Washing Machine (elec.) Hurley Machine Co. U.S. A. 1907
Zip-Fastener W.L. Judson U.S. A. 1891

Important Discoveries
Discovery - Discoverer - Nationality - Year

Aluminium Hans Christian Oerstedt Denmark 1827
Atomic number Henry Moseley England 1913
Atomic structure of matter John Dalton England 1803
Chlorine C.W. Scheele Sweden 1774
Electromagnetic induction Michael Faraday England 1831
Electromagnetic waves Heinrich Hertz Germany 1886
Electromagnetism Hans Christian Oersted Denmark 1920
Electron Sir Joseph Thomson England 1897
General theory of relativity Albert Einstein Switzerland 1915
Hydrogen Henry Cavendish England 1766
Law of electric conduction Georg Ohm Germany 1827
Law of electromagnetism Andre Ampere France 1826
Law of falling bodies Galileo Italy 1590
Laws of gravitation & motion Isaac Newton England 1687
Laws of planetary motion Johannes Kepler Germany 1609-10
Magnesium Sir Humphry Davy England 1808
Neptune (Planet) Johann Galle Germany 1846
Neutron James Chadwick England 1932
Nickel Axel Cronstedt Sweden 1751
Nitrogen Daniel Rutherford England 1772
Oxygen Joseph Priestly, C.W. Scheele England, Sweden 1772
Ozone Christian Schonbein Germany 1839
Pluto Clyde Tombaugh U.S.A 1930
Plutonium G.T. Seaborg U.S.A 1940
Proton Ernest Rutherford England 1919
Quantum Theory Max Planck Germany 1900
Radioactivity Antoine Bacquerel France 1896
Radium Pierre & Marie Curie France 1898
Silicon Jons Berzelius Sweden 1824
Special theory of relativity Albert Einstein Switzerland 1905
Sun as centre of solar system Copernicus Poland 1543 Uranium Martin Klaproth Germany 1789 Uranus (Planet) William Herschel England 1781
X-rays Wilhelm Roentgen Germany 1895

Scientific Instruments
Name of Instrument - Used for

Altimeter measuring altitude
Ammeter measuring strength of an electric current
Anemometer measuring the velocity of wind
Audiometer measuring level of hearing
Barometer measuring atmospheric pressure

Callipers measuring the internal and external diameters of tubes
Calorimeter measuring quantity of heat
Compass finding out direction
Dynamo converting mechanical energy into electrical energy
Galvanometer detecting and determining the strength of small electric currents
Hydrometer measuring specific gravity of a liquid
Hygrometer measuring the humidity in the atmosphere
Lactometer measuring the purity of milk
Manometer measuring the gaseous pressure
Micrometer measuring minute distances, angles, etc.
Microscope seeing magnified view of very small objects
Photometer measuring intensity of light from distant stars
Pyrometer measuring high temperatures
Radar detecting and finding the presence and location of moving objects like aircraft, missile, etc.
Radiometer measuring the emission of radiant energy
Rain Gauge measuring the amount of rainfall
Seismograph measuring and recording the intensity and origin of earthquake shocks
Sextant measuring altitude and angular distances between two objects or heavenly bodies
Spectrometer measuring the refractive indices
Spherometer measuring the curvature of spherical objects/surface
Sphygmomanometer measuring blood pressure
Stethoscope ascertaining the condition of heart and lungs by listening to their function
Stroboscope viewing objects that are moving rapidly with a periodic motion as if they were at rest
Tachometer measuring the rate of revolution or angular speed of a revolving shaft
Telescope viewing magnified images of distant objects
Thermocouple measuring the temperature inside furnaces and jet engines
Thermometer measuring human body temperature
Thermostat regulating constant temperature Ultrasonoscope measuring utrasonic sounds
Viscometer measuring the viscosity of a fluid
Voltmeter measuring potential difference between two points.