Question

An air bubble in a glass slab $(\mu =1.5)$ is 6 cm deep when viewed from one face and 4 cm deep when viewed from the opposite face. The thickness of the glass plate is:

• A. 10 cm
• B. 12 cm
• C. 15 cm
• D. 20 cm

Answer 1

The correct option is C

15 cm

Let the thickness of the slab be $t$ and distance of air bubble from one side is $x$
The refractive index of a medium is also given by $=\frac{\text{Real depth}}{\text{Apparent depth}}$.
When viewed from side (1) : $1.5=\frac{x}{6}\Rightarrow x=9cm$
When viewed from side (2) : $1.5=\frac{(t-x)}{4}\Rightarrow 1.5=\frac{(t-9)}{4}\Rightarrow t=15cm$