Question

An object is placed 30cm from reflecting surface in front of a block of glass 10 cm thick having it's farther side silvered. The final image is formed 23.2 cm behind the silvered face. The refracting index of glass is :

Answer 1

The refractive index of glass n is equal to

$$n = \frac{r}{a} (1)$$

where r is real depth, a is the apparent depth

In our case, r=30 cm

The silvered surface act as a mirror and we can write

$$a + 10 = 23.2 (2)$$

Using (2) we got

$$a = 13.2 (3)$$

We put (3) in (1)

n=2.27

Answer:

2.27