photo.jpg

# General Science ## Part-1: Physics ### Work 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 ene...

# General Science ## Part-1: Physics ### Work 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 × 10⁶ joule * 1 HP = 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⁄s². * 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 one-sixth 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.