Complex amplitude of E-field and phase changes

[km707]

Hi,

I'm looking through my notes on em waves in dielectrics and the fresnel equations and I've been stuck on this for a while.

It states that if the complex amplitude = E₀e^iΦ is positive there is no phase change. However when the value is negative, the phase change Φ is π.. Why is that?

Thanks in advance!

 

[Niles]

It just means that after reflection from the surface of an insulator, then the reflection coefficient (the fraction between the incoming and reflected amplitude) might be either negative or positive. If positive, there is no phase change. If it is negative, then it means that the reflected E-field "points the other way" compared to the incoming E-field - which is just a π-change in phase (recall exp(iπ) = -1).