Light in moving media

From Wikiversity
Jump to navigation Jump to search

Requisites[edit | edit source]

Relativistic addition of velocities

Refractive index

Problem[edit | edit source]

Light moves through a slowly moving medium with refractive index n. That medium moves with a speed v in parallel with the direction of light. What speed will be measured for that light by a rest observer?

Solution[edit | edit source]

If we have a medium with refractive index n, the speed of light relative to that medium is c/n.

Using relativistic addition of velocities, we get for the rest observer:

But as , we can expand that expression in terms of :

The factor was known as the Fresnel drag coefficient. It is easily measured with interference experiments.

Generalization[edit | edit source]