Question

A ray of light is incident on an equilateral prism in such a way that the angle of incidence is equal to the angle of emergence and each is equal to 3/4 of the prism angle. The angle of deviation for the ray of light is

• A. ${45}^{\circ }$
• B. ${30}^{\circ }$
• C. ${39}^{\circ }$
• D. ${20}^{\circ }$

Answer 1

The correct option is B ${30}^{\circ }$

As angle of incidence is equal to the angle of emergence the prism is set in minimum deviation position

${\delta }_{min}=i_i+i_e-A=\frac{3}{4}(60+60)-60={30}^o$.