The phase velocity of waves propagating in a hollow metal waveguide is

Question

Question

This question was previously asked in

ESE Electronics 2014 Paper 1: Official Paper

Attempt in App

Answer 1

Concept:

Phase velocity is defined as:

β is the phase constant defined as:

Using where c = speed of light, the above expression becomes:

Also

Using , we get:

Since -1 ≤ cos θ ≤ 1

∴ V_p > c

Extra Information:

Group velocity is given by:

V_g = c cos θ

V_g < c

Conclusion: ∴ The phase velocity is always greater than the speed of light and group velocity is always less than the speed of light.