Question

Speed of light is maximum in:
(A). Glass
(B). Vacuum
(C). Water
(D). Nylon

Answer 1

- Hint: The speed of light depends on the medium in which it is travelling. Light moves slowly in an optically denser medium.

Complete step-by-step solution -

The refractive index of the material is defined as the ratio of the velocity of light in a vacuum to the velocity of light in other mediums. The refractive index is always greater or equal to one. It is dimensionless in nature and is denoted by ‘n’.
$\text{n=}\dfrac{\text{c}}{\text{v}}$
Where,
n is the refractive of a particular medium.
c is the velocity of light in vacuum.
v is the velocity of light in a particular medium.
A medium having higher refractive index is called an optically denser medium, a medium which is having a lower refractive index is called an optically rarer medium. Light travels fast in an optically rarer medium. If we consider the refractive of materials given in the options, we can see that the refractive index of nylon is 1.525, refractive index of water is 1.33 while the refractive index of glass is 1.55 and the refractive index of vacuum is 1. So from these values it is clear that the refractive index of vacuum is lower than any refractive index. So light will travel faster in vacuum.
Light shows maximum velocity in vacuum. So there is vacuum in the options, you can be sure that it is the medium through which light travels faster. Air also has a refractive index very close to one (n=1.003) but not less than vacuum.

So the answer to the question is option (B)- vacuum.

Note: The speed of light in a vacuum is exactly 299792458 meters per second, which can be approximately written as $3\times {{10}^{8}}\text{ m/s}$.