Question

a ray of light striking plane mirror at angle i then deviation suffered by the plane mirror is 40degrees then i

Answer 1

Angle of incidence is the angle made by light ray with the vertical line drawn from the point where it lands on the mirror. This is 90 - 40 = 50°.

Now:

Angle of incidence = Angle of reflection = 50°

So, light bends by 50 + 50 = 100°