A ray of light strikes a plane mirror PQ at an angle of incidence of 30∘, is reflected from the plane mirror and then strikes a second plane mirror QR placed at right angles to the first mirror. The angle of reflection at the second mirror is : (a) 30∘ (b) 45∘ (c) 60∘ (d) 90∘ Draw a ray-diagram to illustrate your answer.