# How to measure the polarization density

1. Mar 19, 2010

### netheril96

All I know is that polarization density satisfies two equations
$$$\begin{array}{l} \rho _{bound} = - \nabla \cdot \vec P \\ \sigma _{bound} = \vec n_{out} \cdot \vec P \\ \end{array}$$$
This is the divergence and boundary conditions of P.But to determine a vector field uniquely,one need more than those;at least we should know the curl.

So how can we directly measure or calculate from other quantities the polarization density?
Don't tell me that for homogeneous dielectrics,P is proportional to E.That must have been tested by experiments,too.The question is HOW to prove this by experiment.