Q124 / 160 · WBJEE 2012 · Physics

If the velocity of light in vacuum is $3 \times 10^{8} \mathrm{ms}^{-1}$, the time taken (in nanosecond) to travel through a glass plate of thickness $10 \mathrm{cm}$ and refractive index 1.5 is

Correct answer
A
0.5
B
1
C
2
D
3

Solution

Given $v=3 \times 10^{8} \mathrm{ms}^{-1}, d=10 \mathrm{m}$ and $\mu=1.5$ Here, $t=\frac{d}{c / \mu}$ $$ t=\frac{10 \times 10^{-2}}{2 \times 10^{8}} $$ $\left(\therefore \frac{c}{\mu}=\frac{3 \times 10^{8}}{1.5}=2 \times 10^{8} \mathrm{ms}^{-1}\right)$ $t=0.5 \times 10^{-9} \mathrm{s}$

Hence, the correct answer is option: 'A'.

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