Ray Optics and Optical Instruments - Result Question 20

20. Light travels through a glass plate of thickness $t$ and refractive index $\mu$. If $c$ is the speed of light in vacuum, the time taken by light to travel this thickness of glass is

[1996]

(a) $\mu t c$

(b) $\frac{t c}{\mu}$

(c) $\frac{t}{\mu c}$

(d) $\frac{\mu t}{c}$

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Answer:

Correct Answer: 20. (d)

Solution:

  1. (d) Total thickness $=t$; Refrative index $=\mu$ Speed of light in Glass plate $=\frac{c}{\mu}$

Time taken $=\frac{t}{(\frac{c}{\mu})}=\frac{\mu t}{c}$.

where, $t=$ thickness of glass plate

Speed of light in medium

$\nu=\frac{\text{ Speed of light in vaccum }}{\mu \text{ of medium }}$