The discussion revolves around the phase velocity and group velocity of electromagnetic (EM) radiation in free space, specifically questioning their values and relationships. Participants explore the definitions and equations related to these concepts.
The discussion is ongoing, with participants providing insights into the relationships between phase and group velocities. Some guidance has been offered regarding the correctness of the equations used, and there is an exploration of the implications of frequency dependence on wave speed.
Participants are navigating the assumptions that phase and group velocities may differ in general cases, but are specifically addressing the scenario of EM waves in a vacuum where these velocities are equal.
They are the same: cZedCar said:Homework Statement
(i) What is the phase velocity of EM radiation in free space?
(ii) What is its group velocity?
Andrew Mason said:They are the same: c
AM
The equation is correct: VpVg = c^2 ; Vp=Vg=cZedCar said:So is the eqn which I have referred to, and used for my solution, the incorrect one to use on this occasion?
Andrew Mason said:The equation is correct: VpVg = c^2 ; Vp=Vg=c
AM
You cannot conclude that Vp = c from the equation: VpVg=c2. You would have to know that the phase velocity of light in a vacuum is equal to the group velocity.ZedCar said:Since, as you have above Vp=Vg=c, does that mean I can further reduce the two solutions I had in my original post from
(i) Vp = (C^2)/Vg
(ii) Vg = (C^2)/Vp
to
(i) Vp = c
(ii) Vg = c
Andrew Mason said:You cannot conclude that Vp = c from the equation: VpVg=c2. You would have to know that the phase velocity of light in a vacuum is equal to the group velocity.