### Define the following

1. Refraction.
Ans. The phenomenon of change in the direction of light when it passes from one transparent medium to another is called refraction.
2. Refractive index.
Ans.
For a given pair of media, the ratio of the sine of the angle of incidence to

the sine of the angle of refraction is constant. This constant is called as refractive index.
If ‘i’ is the angle of incidence and ‘r’ is the angle of refraction then,

sin i
sin r = Constant.

3. Dispersion of light.
Ans.
The phenomenon of splitting of light into its component colours is dispersion.

4. Spectrum.
Ans.
The band of coloured components of a light beam is called its spectrum.

5. Scattering of light.
Ans.
When a ray of light is incident on extremely small particles, the particles

deflect the light in different directions. This phenomenon is scattering of
light.
6. Absolute refractive index.
Ans.
If medium first is vacuum then refractive index of medium second is called

as absolute refractive index.