Question

A beam of light is converging towards a point I on a screen. A plane parallel plate of glass whose thickness is in the direction of beam = t, refractive index = n is introduced in the path of the beam. The convergence point is shifted by …… 

(A) t[1 + (1/n)] never 

(B) t[1 – (1/n)] nearer 

(C) t[1 + (1/n)] away 

(D) t[1 – (1/n)] away

Answer 1

The correct option is (B) t[1 – (1/n)]nearer

Explanation:

When glass plate of thickness t is introduced, the optical path increases by (t/n). So the convergence point shifts by t – (t/n) i.e. t[1 – (1/n)] nearer.