Question

An equilateral prism deviates a ray through ${45}^{\circ }$ for the two angles of incidence differing by ${20}^{\circ }.$ The angle of incidence is

• A. ${62.5}^{\circ }$
• B. ${42.5}^{\circ }$
• C. Both are correct
• D. Both are wrong

Answer 1

The correct option is C Both are correct

First angle of incidence $=i_1=i$

Second angle of incidence $i_2=i_1+{20}^{\circ }$

Angle of deviation, $d=i_1+i_2-A$ where A is angle of prism.

$45=2i+20-60$

$i=42.5$

$i_2=i+20=62.5$

Hence both are correct.