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)

away from the lens by $\left(1-\frac{1}{\mu} \right)x$

Answer 2

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 $\left[x-\frac{x}{\mu}\right]=x\left(1-\frac{1}{\mu}\right)$