Question

A ray of light enters into benzene from air. If the refractive index of benzene is 1.50, by what percent does the speed  of light reduce on entering the benzene?

Answer 1

Answer: 33.3 %

Explanation:

When the light enters from rarer medium to denser medium, its speed reduces. The ratio of the speed of light in the two media gives the refractive index of the medium.

Refractive index, $\mu =\frac{v_{air}}{v_{medium}}$

$\mu=1.50$  (given for Benzene)

speed of light in air, $v_{air}=3\times10^8m/s$

Hence, speed of light in the medium,

$v_{medium}=\frac{3\times10^8m/s}{1.50} = 2\times 10^8 m/s$

The percentage of speed of light reduces $= \frac{3\times10^8m/s-2\times10^8m/s}{3\times10^8m/s}\times 100\%=33.3\%$

Hence, the speed of light reduces by 33.3 % on entering Benzene.

Answer 2

Answer:

33.3 % .

Explanation:

Given :

Refractive index of benzene = 1.50

We know :

Speed of light = 3 × 10⁸ m / sec

We know formula for n :

n = speed of light in vacuum / speed of light in benzene

n = c / v

1.5 = 3 × 10⁸ / v

v = 2 × 10⁸ m / sec

Now ,

Percentage ( % ) decrease = 1  × 10⁸ / 3  × 10⁸  × 100 %

% decrease = 33.3 % .

Therefore , we get required answer.