Simple Question: Speed of Electromagnetic Waves in a Medium

optics electromagnetic-radiation speed-of-light refraction

1,660

As for $\mu$ or $\varepsilon$, not necessarily, this only means that $\sqrt{\frac{\varepsilon\mu}{\varepsilon_0\mu_0}}=1$ at the specific frequency. This is possible, e.g., if $0<\mu<1$. The above is about phase velocity, although, as far as I understand, your statement is not necessarily true for group velocity either. As for the velocity of the front of the wave, it is always equal to the velocity of light in vacuum, as far as I remember. As for $n$, yes, your statement seems correct (at least if we do not consider losses in the medium).

1,660

Bob Riley

Updated on August 01, 2022

Comments

Bob Riley 10 months

If the speed of an electromagnetic wave in a particular medium is such that $v = c$, the speed of light, does this mean that the permeability $\mu = \mu_0$, i.e. that of a vacuum and the index of refraction is also $n = \frac{c}{v} = 1$? Also $\epsilon = \epsilon_0$?
- newera about 10 years
  
  when the light moves in vaccum, the value of epsilon is ofcourse equal to epsilon nought.
Admin about 10 years

As for the velocity of the front of the wave, it is always equal to the velocity of light in vacuum I don't think this is right. It sounds like you're talking about the signal velocity: en.wikipedia.org/wiki/Signal_velocity The signal velocity is usually equal to the group velocity, which is usually less than c.
akhmeteli about 10 years

@Ben Crowell: en.wikipedia.org/wiki/Front_velocity
Admin about 10 years

I see, +1. I hadn't been aware of precursor signals.