A ray of light is incident on an equilateral prism at an angle of 45° and is refracted parallel to the base of the prism. The angle of deviation would be

30°

The correct answer is Option (2) → 30°

Given:

• Angle of incidence, $i = 45^\circ$
• The prism is equilateral: angle of prism, $A = 60^\circ$
• The refracted ray travels parallel to the base, so the angle of refraction inside the prism is $r = 30^\circ$

Using the angle of deviation formula for a prism:

$\delta = i + e - A$

Since the ray travels parallel to the base, the emergent angle $e = i = 45^\circ$

$\delta = 45^\circ + 45^\circ - 60^\circ$

$\delta = 90^\circ - 60^\circ = 30^\circ$

Final Answer: $30^\circ$