Question

An air bubble in a glass slab with refractive index $1.5$ (near normal incidence) is $5cm$ deep when viewed from one surface and $3cm$ deep when viewed from the opposite face. The thickness (in $cm$) of the slab is

• A. 12
• B. 16
• C. 8
• D. 10

Answer 1

The correct option is A 12

The apparent depth of bubble as seen from one surface = $\frac{d_1}{\mu }=d_{app1}=5cm$
$⟹$ Real depth of bubble from one surface $d_1=7.5cm$

Similarly, real depth of bubble from other surface $d_2=1.5\times 3cm=d_{app2}=4.5cm$

Hence the thickness of the glass is $d_1+d_2=12cm$