A parallel beam of light is incident from air at an angle α on side PQ of a right-angled triangular prism of refractive index n = √2. Light undergoes total internal reflection at face PR when α has a minimum value of 45°. The angle θ of the prism is:

Question

G1 Physics · Accepted Answer

Derived solution: Step 1: For a prism use r₁ + r₂ = A and δ = i + e - A. At minimum deviation i = e and r₁ = r₂ = A/2, so μ = sin[(A + δₘ)/2]/sin(A/2). Step 2: Substitute the values given in the question and apply the geometry/sign convention shown. Step 3: On simplification the result is 15°. Therefore the correct option is A.