Chapter 9 Ray Optics and instrument Class12 Physic, Chapter9 Ray Optics & Instrument | Page 2

Light
Light is a form of energy eyes . which produces the Sources of light are of three types-thermal sources and luminescent sources .
Photometry is a branch measurement of light energy .
Characteristics of Light
Light waves are electromagnetic waves , whose nature is transverse . The speed of light in vacuum is 3 x 10 8 mls but it is different in different media .
The speed and wavelength of light change when it travels from one medium to another but its frequency remains unchanged .
Important Terms
( i ) Luminous Objects The objects which emits its own light , are called luminous objects , e . g ., sun , other stars , an oil lamp etc .
( ii ) Non-Luminous Objects The objects which do not emit its own light but become visible due to the reflection of light falling on them , are called nonluminous objects , e . g ., moon , table , chair . trees etc .
( iii ) Ray of Light A straight line drawn in the direction of propagation of light is called a ray of light .
( iv ) Beam of Light A bundle of the adjacent light rays is called a beam of light .
( v ) Image If light ray coming from an object meets or appear to meet at a point after reflection or refraction , then this point is called image of the object .