Question

Time taken by light to pass through 4 mm thick glass slab of refractive index 1.5 will be :

• A. $8\times {10}^{-11}s$
• B. $2\times {10}^{-11}s$
• C. $8\times {10}^{-8}s$
• D. $2\times {10}^{-8}s$

Answer 1

Answer: (B)

$2\times {10}^{-11}s$

We have time taken,

$t=\frac{distancetravelled}{speed}=\frac{thicknessoftheslab}{\frac{c}{\mu }}$

where, $\mu$ is the refractive index and $c$ is the velocity of light.

Given, $\mu =1.5$ and thickness $=4mm=4\times {10}^{-3}m$

$⟹t=\frac{4\times {10}^{-3}\times 1.5}{3\times {10}^8}=2\times {10}^{-11}s$