Question

A bubble in glass slab $(\mu =1.5)$ appears at $5\text{cm}$ when viewed from one side and at $2\text{cm}$ when viewed from opposite side. The thickness of the slab is:

• A. $13.5\text{cm}$
• B. $12.5\text{cm}$
• C. $10.5\text{cm}$
• D. $11.5\text{cm}$

Answer 1

The correct option is C $10.5\text{cm}$


Let ${}^{\prime }{t}_1^{\prime }$ and ${}^{\prime }{t}_2^{\prime }$ be the real depth of bubble from both sides.

Here, ${\mu }_g=\frac{\text{Real depth}}{\text{Apparent depth}}$

$\Rightarrow {\mu }_g=\frac{t_1}{{\left(d_{app}\right)}_1}$

or $t_1=1.5\times 5=7.5\text{cm}$

Similarly,
${\mu }_g=\frac{t_2}{{\left(d_{app}\right)}_2}$

or, $t_2=1.5\times 2=3\text{cm}$

So, the thickness of the slab is,
$t=t_1+t_2$
$\therefore t=7.5+3=10.5\text{cm}$

Why this question? Tips: Thickness of slab will be equal to the sum of real depths of bubble from the both sides of slab.