Question

What is refraction of light ? How is it related to refractive index ?

Answer 1

Refraction is the bending of a wave when it enters a medium where its speed varies. when refraction of light passes from a fast medium to a slow medium it bends the light ray toward the normal to the boundary between the two media and the amount of bending depends on the indices of refraction, it is is described quantitatively by Snell's Law.

Refractive index of a material is a measure of the change in speed of light as it passes from a vacuum into the material.

If $i$is the angle of incidence of a ray in vacuum (angle between the incoming ray and the perpendicular to the surface of a medium, called the normal) and $r$is the angle of refraction (angle between the ray in the medium and the normal), the refractive index $n$is defined as the ratio of the sine of the angle of incidence to the sine of the angle of refraction.

i.e., $n=\frac{\sin i}{\sin r}$

Refractive index is also equal to the velocity of light $c$ of a given wavelength in empty space divided by its velocity $v$ in a substance.

or $n=\frac{c}{v}$