# Homework Help: Dipole in electric field, capacitor

1. Mar 28, 2004

### burak_ilhan

a parallel plate capacitor is filled with a layer of distilled water of 0.3cm tihck. The dipole moment of a water molecule is 6.1*10^(-30) C.M. Assume that the dipole moments of the water molecules are all perfectly aligned with the electric field. What is the surface charge density of bound charges on the surface of the layer of water.(dielectric constant of water:80).

Well, I solved lots of problems like that except with a dipole moment. I dont know where to use that. I tried to use some energy relations but no results. Thanks for any help.

2. Mar 29, 2004

### himanshu121

surface charge density $$\sigma$$
$$\sigma _{bounded} = \sigma _{free} [ 1-\frac{1}{\epsilon _{r}}]$$

3. Mar 29, 2004

### burak_ilhan

Thanks but I know that formula, and I bet everybody knows... I need a way to solve the problem.:)