17
Symmetry
17.1 Conservation of Momentum and Apparent Refractive Index
If we refract a light ray with momentum p1 at a surface with normal n, and it comes out as a ray with momentum p2 after refraction, p2 and p1 are related (see Chapter 16) by
where n1 and n2 are the refractive indices before and after refraction. If we had a reflection, instead of refraction, the reflected ray would have momentum
where n is the refractive index of the material in which the reflection occurs. In any case, we can write
where σ is a scalar.
We now consider a different situation in which we have the general coordinate ...
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