Exam (elaborations) r UPSC 21098

Work is said to be done, if force acting on a body is able to actually move it through some distance in the direction of the force. Its SI unit is a joule. ENERGY • Energy is a scalar quantity and its unit is Joule. • The sum of all kinds of energies in an isolated system remains constant at all times. This is the law of conservation of energy. POWER Its unit is watt. • 1 watt hour = 3600 Joule • 1 kilowatt hour = 3.6 x 106 joule • 1HP = 746 watt GRAVITATION • Everybody in the universe attracts other body by a force called force of gravitation. • The gravitational force of the earth is called gravity. • The acceleration produced in a body due to force of gravity is called acceleration due to gravity (g) and its value is 9.8 m/s' • Acceleration due to gravity is independent of shape, size and mass of the body. • Escape velocity is the minimum velocity with, which an object just crosses the Earth's gravitational field and never returns. Escape velocity at the Earth's surface is 11.2 km/s. • Escape velocity at the Moon's surface is 2.4 km/s. Due to low escape velocity there is no atmosphere on the moon. • Value of g decreases with height or depth from Earth surface. • g is maximum at poles. • g is minimum at equator. • g decreases due to rotation of Earth. • g decreases if angular speed of Earth increases and increases if angular speed of Earth decreases. • The acceleration due to gravity at the moon is onesixth that of the Earth. So, the weight of a person on the surface of the moon will be 1/6 of his actual weight on the Earth. SATELLITE • Satellites are natural or artificial bodies revolving around a planet under its gravitational force of attraction. • Moon is a natural satellite, while INSAT-B is an artificial satellite of Earth. • The period of revolution of satellite revolving near the surface of earth is 1 hour 24 minutes (34 minutes). • Geo-stationary satellite revolves around the Earth at a height 36000 km (approx). • Time period of rotation of geo-stationary satellite is 24 hours. • The Earth rotates on its axis from West to East. This rotation makes the Sun and the stars appear to be moving across the sky from East to West. • A geosynchronous satellite is a satellite in geosynchronous orbit, with an orbital period the same as the Earth's rotation period. • A special case of geosynchronous satellite is the geostationary satellite, which has a geostationary orbit – a circular geosynchronous orbit directly above the Earth's equator. • Geo-stationary satellite is used to telecast. TV programmes from one part of the world to another, in weather forecasting, in predictions of floods and droughts. • Polar Satellite Revolves around the earth in polar orbit at a height of 800km (app.) Time periods of these satellites is 84 min. ATOMIC AND NUCLEAR PHYSICS Cathode Rays Cathode rays, discovered by Sir William Crooke and its properties are • travel in straight lines. • Produce fluorescence. • can penetrate through thin foils of metal and deflected by both electric and magnetic fields. • have velocity ranging 1/30th to 1/10th of the velocity of light. (3) Positive or Canal Rays • These rays were discovered by Goldstein. • The positive ray consists of positively charged particles. • These rays travel in straight line. • These rays are deflected by electric and magnetic fields. • These rays can produce ionization in gases. X-Rays • X-rays are electromagnetic waves with wavelength range 0.1 A-100 A. • X-rays were discovered by Roentgen. • X-rays travels in straight line. • Long exposures of X – rays in injurious for human body. • X – rays shows photoelectric effect. Uses of X-Rays • In medical sciences X-rays are used in surgery for the detection of fracture, diseased organs, foreign matter like bullet, stones etc. They are used in treatment of cancer and in skin diseases. • In Engineering, X-rays are used in detecting faults, cracks, flaws and gas pockets in the finished metal products and in heavy metal sheets. • In Scientific Work, X-rays are used in studying crystal structure and complex molecules. • In Custom Department X-rays are used in custom department for detection of banned materials kept hidden. Radioactivity • Radioactivity was discovered by Henry Becquerel, Madame Curie and Pierre Curie for which they jointly won Nobel Prize. Nuclear Fission • Atom Bomb is based on nuclear fission. U235 and Pu239 are used as fissionable material. • Nuclear fission was first demonstrated by Halin and Fritz Strassmann. Nuclear Fusion • When two or more light nuclei combined together to form a heavier nucleus is called as nuclear fusion. • For the nuclear fusion, a temperature of the order of 108 K is required. • Hydrogen Bomb was made by the American Scientist in 1952. This is based on nuclear fusion. It is 1000 times more powerful than atom bomb. Nuc