Question

Figure shows a ray of light passing through a prism. If the refracted ray QR is parallel to the base BC, show that (1) r₁ =  r₂ = A/2, (ii) angle of minimum deviation, D or D_m = 2i - A.

Answer 1

(i) From given figure, A = r₁ + r₂  

As the ray QR is parallel to the base BC,

then r₁ = r₂, and i = e

Therefore, 2r₁ (or 2r₂) = A