Question

A glass block of length 18 cm and refractive index 1.5 contains a small bubble. Viewed from one side the bubble appears to be 8 cm from this side. How far in the block will it appear to be when viewed from the opposite side?

Answer 1

Refractive index = real depth/apparent depth

Let the bubble is at distance x from the side F₁ of the glass block.

$1.5 = \frac{x}{8}$

$x = 12\; cm$

The bubble is at distance ($18-12 = 6 \;cm$ ) opposite side F₂ of the glass block.

Let the y is apparent depth when viewed from the side F₂ of the glass block.

$1.5 = \frac{6}{y}$

$y = 4 \;cm$

Answer: 4 cm