# Bound and Free Charge in conductor and dielectric

1. Nov 20, 2008

### FourierX

I am reading an electrodynamics book to grasp the concept of bound and free charge, esp in conductor and dielectric. I got lost with the text on the book. Can anyone please help me understand the concept well?

2. Nov 20, 2008

### Staff: Mentor

I bet some people here could help... what specific questions do you have?

3. Nov 20, 2008

### Staff: Mentor

A free charge can move in response to an externally supplied force while a bound charge cannot.

4. Nov 20, 2008

### gabbagabbahey

Free charges are free to move about the entire medium, while bound charges are restricted to moving in small 'loops' around whichever molecule/ atom they are bound to.

5. Nov 20, 2008

### tiny-tim

For a bit more detail, click free charge for the PF Library item

6. Nov 21, 2008

### FourierX

thanks

in case of a wire carrying a certain amount of charge, say Q, which is insulated by a insulator (dielectric), I read that the bound charge on the outer surface and inner surface of the insulator is equal to each other in magnitude. But I could not derive it myself. My approach was to use Guass's law for D, but i did not get what enclosed free charge was. In such a case, how does the equation $$\rho$$ = $$\rho$$b + $$\rho$$f hold true?