Question

State the laws of refraction of light. Give an expression to relate the absolute refractive index of a medium with speed of light in vacuum.

Answer 1

Snell's law of reflection of light states that:
1. The ratio os sine angle of incidence to sine angle of refraction is constant i.e. sin i/sin r =canstant
2. The refracted ray, incident ray and normal lie on the same plane and at the same point.
According to the Snell's law,
The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant.
Sine of angle of incidence(i) /sine of angle of refraction (r) =constant
this constant is called refractive index(n).
$a_{n_w}=\frac{n_w}{n_a}$
This is the expression for the refractive index of water with respect to the air.
Absolute refractive index of a medium =Speed of light in vacuum /Speed of light in medium
let the speed of light in air be x
Refractive index of glass =speed of light in air/speed of light in glass
$\frac{3}{2}=\frac{x}{2}\times {10}^{8}m{s}^{-1}x=3\times {10}^{8}m{s}^{-1}x=3\times {10}^{8}m{s}^{-1}$
speed of light in air =$3\times {10}^{8}m{s}^{-1}$