Question

A horizontal ray of light passes through a prism of index 1.50 and apex angle 4° and then strikes a vertical mirror, as shown in the figure (a). Through what angle must the mirror be rotated if after reflection the ray is to be horizontal?

विकल्प

• 1°

• 2°

• 2.5°

• 1.5°

Answer 1

1°

Explanation:

Because the apex angle is so small (α = 4°), the angle of deviation and can be calculated roughly as follows:

δ = (n - 1)α

= (1.5 - 1) × 4°

= 2°.

Fig. (b)

According to Fig. (b), in order for the reflected ray to be horizontal, the mirror must be rotated clockwise through an angle γ given by

γ = `delta/2`

= 1°