Question

The angle between the incident ray and the surface of a plane mirror is 20'. What is the total angle rotated by the incident ray?
I don't understand the question. Needing an explanation.

Answer 1

Angle made by the light ray with the surface of mirror is given as

$\theta_i = 90 - 20 = 70$degree

now as we know as per law of reflection that

angle of incidence = angle of reflection

So here we can say that

$\theta_i = \theta_r$

$\theta_r = 70 degree$

now the total angle that reflected ray will rotate with respect to incident ray is known as angle of deviation

$\delta =180 - \theta_i - \theta_r$

$\delta = 180 - 70 - 70 = 40 degree$

so here reflected light will deviate by total angle of 40 degree fron its incident ray.