Question

Light travels through a glass plate of thickness $t$ and refractive index $n$. If $c$ is the velocity of light in vacuum, then the time taken by light to travel the thickness of the plate will be:

• A. $\frac{nt}{c}$
• B. $\frac{t}{nc}$
• C. $\frac{tc}{n}$
• D. $\frac{c}{nt}$

Answer 1

The correct option is A

$\frac{nt}{c}$

Velocity of light in a medium, $v=\frac{c}{n}$
where, $n$ is the refractive index, $c$ is the velocity of light in vacuum.
Distance travelled = thickness = $t$

Therefore,
Time $=\frac{t}{v}=\frac{nt}{c}$