Question

P is a point on the axis of a concave mirror. The image of P, formed by the mirror, coincides with P. A rectangular glass slab of thickness t and refractive index μ is now introduced between P and the mirror. For the image of P to coincide with P again, the mirror must be moved

(a) towards P by (μ - 1)t 

(b) away from P by (μ - 1)t 

(c) towards P by t(1 - 1/μ) 

(d) away from P by t(1 - 1/μ)

Answer 1

Correct Answer is: (d) away from P by t(1 - 1/μ)

When the slab is introduced between P and the mirror, the apparent position of P shifts towards the mirror by t(1 - 1/μ). Hence, the mirror must be moved in the same direction through the same distance.