221.

A ray of light is incident at an angle i on a glass slab of refractive index µ. The angle between reflected and refracted light is 90°. Then, the relationship between i and µ is

• $\mathrm{i} = {\tan }^{-1} \left(\frac{1}{\mathrm{\mu }}\right)$

• tan i = µ

• sin i = µ

• cos i = µ

When light is refracted from a surface, which of its following physical parameters does not change ?

• Velocity

• Amplitude

• Frequency

• Wavelength