Chapter - 1
Energy

Points to remember:
1. Energy - is the ability to do work. Its S.I. unit is Joules (J). It is a solar quantity.
The Commercial unit of energy is kWhr.
2. Heat Engine - a device which converts heat energy into mechanical energy or work.
3. Types of Heat Engines

4. Internal combustion engines are small & more efficient than steam engines. These are also safer and take a smaller time to start.
5. Efficiency of Heat Engine- extent to which the engine converts the heat energy into mechanical work. It is expressed in percentage.
6. Transformation of energy - the changing of one form of energy into another.
7. Law of conservation of energy - Energy can neither be created nor be destroyed. It can change from one form to another. The total energy of the universe remains constant.
8. Joule's Experiment - Established the relationship between quantity of heat produced by a certain amount of mechanical work.
Conclusion - Heat energy and mechanical energy are equivalent.
9. Mechanical equivalent of heat - It is defined as ratio of mechanical work done to the amount of heat produced.

J = W/Q, where: w - mechanical work done.
Q - heat produced.

10. Simple machine- a device, which is used to do work more conveniently but it, does not produce energy.
11. Mechanical work - is said to be done, if a body moves through a certain distance under the application of a force.
Its S.I. unit is joule, it is a scalar quantity.
12. Power - Rate of doing work or supplying energy. Its S.I. unit is Watt.
13. Solar Heating device - A device which collects in a small region a large amount of heat form sunlight & restricts the loss of heat from that region.
14. Solar cell - A device, which converts solar energy directly into electrical energy.

Important formulas

1. If we denote work done, force applied and distance moved in the direction of force as W,F,S then W = FS
2. P = w/t or E/t where P - Power, W = work done.

3. W = mgh where W - Work done against gravity,

4. KE = 1/2 mv², where KE - Kinetic energy, m - mass
v = velocity respectively.

5. PE = mgh, where PE - Gravitational potential energy

6. Efficiency of heat engine (n)

n = W/Q , W - mechanical work done , Q - heat supplied

7. Heat absorbed or given out (Q) = mst
where m= mass, s= specific heat of substance t= change in temperature.

Class - X, Physics
Ch - 2
SUN AND NUCLEAR ENERGY

Points to Remember
1. All available source of energy can be classified into Renewable and Non- Renewable sources.
2. Solar Energy - Energy liberated by sun in the form of e.m. radiation.
Secret of sun's energy - In the sun small deuterium nuclei fuse together to form bigger nuclei of Helium.
3. Composition of Sunlight - sunlight consists of three types of radiations

4. Spectrum analysis - A methods by which elements present in a body can be identified by studying the wavelength of light it emits.
5. Nuclear Energy - energy released in nuclear reactions.
6. Einstein's Law of conservation of matter & energy - sum total of matter and energy in the Universe remains constant though one can be transformed into another.

7. Isotopes - atoms of the same element of light having the same atomic number but different mass number.
8. Radioactivity - The phenomenon of emission if invisible radiations like a - rays, b - rays and gamma rays by unstable nuclei of heavy elements.
9. Forces operating inside the nucleus - of an atom
a) Nuclear force of attraction
b) Electrostatic force of repulsion
10. Nuclear Fission - the process of a heavy nucleus breaking into medium weight nuclei with the release of a large amount of energy.
11. Nuclear Fusion - Two or more lightweight nucleai fuse together to form a relatively heavy nucleus with the release of large amount of energy.
12. Chain reaction - a reaction in which the particle, which initiates the reaction, is also produced during the reaction.
13. Enrichment - the process of increasing the percentage of U - 235 in natural Uranium.
14. Nuclear reactor - a device in which controlled fission takes place and nuclear energy is converted into heat energy.
15. Coolant - substance which transfers heat energy from Nuclear Reactor to Heat Exchanger.
16. Moderator - A substance which slows down the speed of neutrons in a nuclear reactor to cause fission of U - 235 effectively.
17. Controlling rods - Rods of cadmium and Boron, which absorbs excess of neutrons and thus control chain reaction.
18. Nuclear wastes - The discarded material of nuclear industry, which are potential health hazards.
19. Energy crisis - The situation when energy consumption is faster than energy production.

Class X, Physics
Chapter - 3
Universe

POINTS TO REMEMBER

1. Light & Parsec - Astronomical unit of distance.
2. 1 Light year - 9.46 x 10² km.
3. 1 Parsec = 3.26 Light year = 3.09 x 10¹³ km.
4. Galaxy - a cluster or group of billions of stars. Classification of Galaxies - on the basis of shape
a) Spiral
b) Elliptical
c) Irregular
5. Constellation - a small group of stars arranged in recognizable shape and patterns.
6. Stars - are self - luminous balls of gas.
7. Solar System - Includes sun, planets their moons, asteroids, comets, meteors and some other debris.
8. Comet - luminous heavenly objects which revolve around the sun with a long period of revolution. These have a bright head and a tail
9. Asteroids - Small peices of rubble, which revolve around the sun between the orbit of Mars and Jupiter. They are also termed as minor Planets.
10. Meteor - brought streaks of light passing across the sky. They are visible when they enter the earth's atmosphere.
11. A) Birth and evolution of a star

B) Final stage of a star's life
1) White dwarf star
2) Supernova - neutron star or black hole.
12. Differentiation - The organization of molten earth into various layers having different densities.
13. Planetesimals - The left over gases around the sun condensed to form small chunks of matter called planetesimals.
14. Doppler's effect - The apparent change in frequency of a wave emitted by a source whenever there is relative motion between the source and observer.
15. Red shift - When a source of light moves away from the observer, the frequency of light waves decreases so it shifts towards the red side of the visible spectrum.
16. Hubble's Law - the speed (v) of recession of a galaxy is directly proportional to its distance ( r ) from earth.
i.e. v a r, v = Hr where h- Hubble's constant.
17. Expanding Universe - Edwin Hubble found that all galaxies are moving away from each other. The larger the distance between two galaxies faster they move away from each other.
18. Big Bang Theory - About 15 billion years ago a vast explosion occurred. The matter was broken into pieces, which were thrown, with high speeds in all directions forming stars and Galaxies