Question

A light ray enters from air to diamond as shown in figure.The refractive index of diamond is 2.42. The meaning of this statement is : (a) Speed of light in diamond is 2.42 times the speed of light in air.
(b) Speed of light in diamond is 1 2.42 times the speed of light in air. (c) Diamond is 2.42 times lighter than air.
(d) None of the above.​

Answer 1

The meaning of the statement "The refractive index of diamond is 2.42" means:

(b) Speed of light in diamond is 1/2.42 times the speed of light in air.

• We all know, that the refractive index is the velocity of light in vacuum or air to the velocity of light in a given medium. The formula for the refractive index will be $n=\frac{Speed-of-light-in-vacuum}{Speed-of-light-in-a-given-medium}$
• When it is said that the refractive index of diamond is $2.42$ then it can be explained in a way that the velocity or speed of light when it enters will decrease by $2.42$. As we can see that the refractive index in diamond is high therefore the speed has to be low.

Answer 2

The meaning of this statement is (d) None of the above.

Step-by-step explanation:

• When a light ray travels from one medium to another, the speed of light changes because of different densities of the medium. So, light ray bends due to this phenomena called refraction of light.
• Speed of light decreases in medium high densities.
• Speed of light when travels from denser medium to rarer medium, its velocity increases because the refractive index of denser medium is more than refractive index of rarer medium.
• Refractive index $n=\frac{c}{v}$ where c is the speed of light in vacuum or air and v is the speed of light in the medium.
• So, if refractive index of diamond $n=2.42$, then it means that the speed of light in diamond is $2.42$ times slower than the speed of light in air of vacuum.