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    A source of light is referred to as the origin of sensation in vision. A light ray is produced from one particular source. The source through which light is produced is luminous objects. It is capable of producing light rays itself.  Luminous objects : These are sources through which light rays are produced. Examples of luminous objects are : sun, star (which are referred to as self-luminous of nature), firefly or glowworms (which are referred to as self-luminous of living creature), and electric lamp, candle, torch light ,etcetera, (are referred to as man-made or artificial luminous sources).  Non-luminous objects : These are reflective surfaces which when light falls, produce rays of light. Examples of non-luminous objects are : a signboard placed by the roadside, a mirror placed in the sun, etcetera. These objects are classified into :  •Transparent objects :These are objects one can see through and light can also pass through them, e.g. thin clothes, white

       Lenz's law states that the induced current flows in such a direction as to oppose the motion producing it. This is often called Faraday's second law of electromagnetic induction. The law gives the direction of the induced emf when the current in the primary coil is increased.          The direction of the induced current in the secondary coil will be in the opposite direction.  The direction of the induced current in such that it tries to oppose the movement of the magnet towards the solenoid.         The factors on which the magnitude of the induced emf depends on the following: 1.The strength of the magnet (magnetic flux or lines of force linking the circuit.) 2.Number of turns in the coil (solenoid) 3.The distance between the magnet and the coil. 4.The surface area of the coil. 5.The relative speed between the magnet and the coil.        When a metallic sheet, either in a moving magnetic field or in a changing magnetic field occurs, an induc