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## Homework Statement

In a Fabry-perot interferometer, light is reflected back and forth between 2 highly reflecting parallel mirrors, with a nonconducting medium inside. The waves of magnetic and electric field are 90

^{o}out of phase, unlike the case of a wave in free space where they in phase. Develop an argument using Poynting's theorem for why this should be so.

## Homework Equations

## The Attempt at a Solution

I've thought of using

__E__to calculate

__H__and then say that they're out of phase, but then this method isn't based on Poynting's theorem.

Then I've thought of using the eq.:

__E__=

__E__

_{0}exp((-kapper)z+i(kz-wt))

__B__=

__B__

_{0}exp((-kapper)z+i(kz-wt+theta))

to calculate the Poynting vector, S = 1/mu * (

__E__x

__B__), then somehow show that theta is 90

^{o}, but then I don't really know how to do it.