# Is Malus' Law a law, or does it derive from Maxwells equations?

1. Jun 20, 2007

### Tez

Well the question is in the title. Does Malus' Law (http://en.wikipedia.org/wiki/Malus's_law ) follow automatically from Maxwell's equations, or is it really an extra thing put in by hand? In particular I'm interested if there is a purely classical electromagnetic explanation (i.e. without having to go into the quantum mechanics of wither the light or the polarising medium at all...)

2. Jun 20, 2007

### Claude Bile

Malus' law falls naturally out of Jones Calculus.

http://en.wikipedia.org/wiki/Jones_calculus

Jones Calculus basically involves representing an EM wave as a vector, and optical components as matrices, with the matrices defined such that it transforms the incoming EM wave vector in the correct way. For example, a half-wave plate will have a matrix that rotates the incoming vector by 90 degrees.

Jones Calculus falls naturally from the theory of EM-waves, which in turn drops out of Maxwell's equations.

Claude.

3. Mar 20, 2011

### exponent137

Malus law is a quantum law, in principle. Can we calculate it in a quantum way, so for photons? In the above link this not exist.
This was calculated by Brukner, but without imaginary numbers. I am interested in classical derivation?
quant-ph/0212084v1

4. Mar 22, 2011

### A. Neumaier

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