CRITICAL ANGLE FOR DIFFERENT COLOURS OF LIGHT

 CRITICAL ANGLE:

The critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90°.

FACTORS:

The critical angle of a medium depends on

1. The relative refractive index of the denser medium with respect to the rarer medium. Greater the refractive index, smaller the critical angle. 

For example: refractive index of glass is 1.5, critical angle is 42° and for diamond, refractive index is 2.4, the critical angle is 24°

2. The colour(wavelength) of the light. Longer the wavelength, greater  is the the value of the critical angle.

For example:  Red has longest wavelength among seven colours, so it has maximum value of the critical angle for a medium.