Question

The velocity of all colors is maximum in:
A. Water
B. Vacuum
C. Air
D. Glass

Answer 1

Hint: As we know that the speed of light is roughly in the order of $3 \times {10^8} m/s$ and it is greatly affected by the medium in which it is traveling. The speed of light can scatter from the matter of the medium it is traveling.

Complete step by step solution:
We should keep in mind that the speed of light changes while it travels in a different medium. When a light wave propagates through a medium it is obstructed by the atoms of the medium. When the light hits the atom of the medium it is absorbed firstly and then afterward it is re-emitted and this process goes on again and again which takes a certain amount of time to travel. The more the light is obstructed, the slower is the effective average speed. We can show by the formula that the speed of light in a medium can be calculated as
$v = \dfrac{c}{n}$
Here, v is the speed of light in any medium and c is the speed of light in vacuum and n is the refractive index of the medium.
The speed of light would be maximum in a medium that has the lowest refractive index. And we know that in the all above given options, the vacuum has the least value of refractive index which is equal to 1.
The Refractive index for water is 1.333, for air, it is 1.0003, and for glass, it is 1.5.

The speed of light is maximum in the vacuum. Hence, the correct option is (B).

Note:
We must know that the medium in which speed of light is less is the optically denser medium whereas the optically rarer medium is one where the speed of light is maximum. The light scatters less in the rarer medium and that’s why it’s speed is more in the rarer medium.