Question

Calculate the speed of light propagating through diamond. Why does light slowdown traveling through solids as compared to a vacuum?

Answer 1

For diamond, index of refraction = 2.42

Index of refraction of a material is defined as the ratio of the speed of light in the vacuum to the speed of light in the given material.

The speed of light in vacuum = 2.99792458 x 10⁸ m/s

Speed of light in diamond = (2.99792458 x 10⁸ m/s) / 2.42 = 1.23881181 x 10⁸ m/s.........................Answer

In solids or any medium, light slows down because

Light gets absorbed by the molecules in the medium and then re-emitted which leads to excitation of the molecules which cause vibrations, movement of the particles.

This process is very fast and these vibrations are soo small that it cannot be noticed.

Hence, any medium will slow down the speed of the light.