Question

Two plane mirrors at an angle such that ray incident on mirror undergoes a total deviation of 240degree after 2 reflections the angle between the mirrors is​

Answer 1

Given :

The total angle of deviation = 240°

To Find :

The angle between the mirrors after two reflections

Solution :

• The light rays travel as shown in the figure

• From the figure, the sum of angles in a triangle is 180°

        ∅ + (90 - α) + (90-i ) = 180

       180 + ∅ - α -i  = 180

       ∅ =  α + i

• Total deviation = 360 - 2(i+α)

         240 = 360 - 2∅

         2∅ = 120

         ∅  = 60°

   The angle between the morrors is 60°