Question

If the velocity of light in vacuum is $3\times10^{8}\, ms^{-1},$ the time taken (in nanosecond) to travel through a glass plate of thickness $10 \,cm$ and refractive index $1.5$ is

• A. 0.5
• B. 1
• C. 2
• D. 3

Answer 1

Answer: (A)

0.5

Answer 2

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