Question

A converging lens forms a real image $I$ of an object on its principal axis. A rectangular slab of refractive index $\mu$ and thickness $x$ is introduced between $I$ and the lens, $I$ will move

• A. towards the lens $(\mu -1)x$
• B. towards the lens by $\left(1-\frac{1}{\mu }\right)x$
• C. away from the lens by $(\mu -1)x$
• D. away from the lens by $\left(1-\frac{1}{\mu }\right)x$

Answer 1

Answer: (D)

Due to insertion of slab, the optical path increases by $x/\mu$, where $x$ is thickness of slab. Therefore the converging point will shift away by
$\left[x-\frac{x}{\mu }\right]=x\left(1-\frac{1}{\mu }\right)$