Question

An air bubble in a glass slab $(\mu =1.5)$ appears $3cm$ deep when viewed from one face and $4cm$ when viewed from opposite face, then real thickness of glass slab is

• A. $8.5cm$
• B. $9cm$
• C. $9.5cm$
• D. $10.5cm$

Answer 1

The correct option is D $10.5cm$

Measuring all distances from the interface:
$\frac{{\mu }_{\text{object space}}}{\text{object distance}}=\frac{{\mu }_{\text{image space}}}{\text{image distance}}$

For refraction at $\left(1\right)$
$\frac{1.5}{x}=\frac{1}{3}\Rightarrow x=4.5\text{cm}$

For refraction at $\left(2\right)$
$\frac{1.5}{t-x}=\frac{1}{4}\Rightarrow t-x=6$

$t=6+4.5$
$t=10.5\text{cm}$