A ray incident parallel to the principal axis on a concave mirror at an angle θ becomes parallel to the incident ray after two reflections. If θ = π/N rad, find N.

Question

G1 Physics · Accepted Answer

Derived solution: Step 1: Use the spherical-mirror relation 1/f = 1/v + 1/u with m = - v/u and R = 2f, following the Cartesian sign convention. Step 2: Substitute the values given in the question and apply the geometry/sign convention shown. Step 3: On simplification the result is 4. Therefore the correct option is D.