Question

Refractive index of diamonds is 2.42. What do we mean from this?
A.) Speed of light in diamond is raised by a factor 2.42 relative to that in vacuum
B.) Speed of light in diamond is lower by a factor 2.42 relative to that in vacuum
C.) Speed of light in air equals to speed of light in diamond
D.) None of the above

Answer 1

Hint: A light undergoes refraction when it travels from one medium to another. When it travels from a rarer to denser medium, the speed of light reduces while if it travels from a denser to rarer medium, the speed of light increases.

Detailed step by step answer:
The phenomenon of bending of light when it travels from one medium to another is called refraction.

The refractive index can also be defined in terms of the velocity of light in the vacuum and velocity of light in the given medium (in our case it is diamond). It is defined as the ratio of the velocity of the light in air or vacuum and the velocity of light in diamond. So, we can write this expression for diamond in the following way:

$\mu ={\displaystyle \frac{\text{Velocity of light in air or vacuum}}{\text{Velocity of light in diamond}}}=2.42$

The significance of this expression is that the velocity of light in diamond is 2.42 times less than the velocity of light in air or vacuum. We can also say that the speed by light inside a diamond is ${\displaystyle \frac{1}{2.42}}$ times less than the speed of light in air or vacuum.

Note: Refraction is governed by two laws of refraction given below:
a.) The incident ray, the refracted ray and the normal at the point of incidence, all lie in the same vertical plane.
b.) The ratio of the sine of the angle of incidence to the sine of the angle of refraction is called the refractive index given as:
$\mu ={\displaystyle \frac{\sin i}{\sin r}}$
Where $\mu$ is called the refractive index, i is the angle of incidence and r is the angle of refraction.