Question

Show that the group velocity of visible light in fused silica is slower than its phase velocity.

a) The group velocity is always faster.
b) The group velocity is always slower.
c) The two velocities are equal.
d) The relationship depends on the wavelength.

Answer 1

b) The group velocity of visible light in fused silica is slower than its phase velocity.

Step-by-step explanation:

The correct answer is b. The group velocity is always slower. When light travels through a physical medium, its speed is always less than the speed of light. The group velocity refers to the speed at which the peaks of the light waves or the information in the wave packet propagates through the medium. On the other hand, the phase velocity refers to the speed at which the individual wave crests propagate. In materials like fused silica, the group velocity is slower than the phase velocity, which means that the information carried by the light waves travels slower than the individual crests of the waves.