Question

A beam of light is converging towards a point $L$. A plane parallel plate of glass of thickness $t$, refractive index $\mu$ is introduced in the path of the beam. The convergent point is shifted by :

(assume near normal incidence).

• A. $t(1-\frac{1}{\mu })away$
• B. $t(1+\frac{1}{\mu })away$
• C. $t(1-\frac{1}{\mu })nearer$
• D. $t(1+\frac{1}{\mu })nearer$

Answer 1

The correct option is C $t(1-\frac{1}{\mu })nearer$

When glass plate of thickness t is introduced, the optical path increases by $\frac{t}{n}$.

So the convergence point shifts by $t–\frac{t}{\mu }$ i.e. $t[1–\frac{1}{\mu }]$ nearer.