Charge on conducting and non-conducting body

  • #1

Main Question or Discussion Point

the charge on a body can be distributed throughout the entire volume only if the body is non-conducting,and the charge on a conducting body can reside only on the surface. I'm confused , why?
 

Answers and Replies

  • #2
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All charges are surrounded by lines of force (electric fields). If there are charges iwithin conducting bodies, there are also electric fields. But electric fields don't exist in conducting bodies, because if there were, the charges would move (conduct) to cancel the electric fields. Therefore there are no free (excess) charges within conducting bodies. There can be charges on the inside surface of a conducting sphere, but only if there are matching free charges within the enclosed volume. Gauss's theorem in the conducting sphere (integral[E*n da] = integral [rho dv] = 0) requires no electric field within the conducting sphere, so no net enclosed charge. In short, use Gauss's Law.
 
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  • #3
All charges are surrounded by lines of force (electric fields). If there are charges iwithin conducting bodies, there are also electric fields. But electric fields don't exist in conducting bodies, because if there were, the charges would move (conduct) to cancel the electric fields. Therefore there are no free (excess) charges within conducting bodies. There can be charges on the inside surface of a conducting sphere, but only if there are matching free charges within the enclosed volume. Gauss's theorem in the conducting sphere (integral[E*n da] = integral [rho dv] = 0) requires no electric field within the conducting sphere, so no net enclosed charge. In short, use Gauss's Law.
thanks.... i got it ... but why can the charge be distributed throughout the entire volume only for a nonconducting body??/
 
  • #4
Born2bwire
Science Advisor
Gold Member
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Because the charges are generally thought of as being bound to the atoms/molecule that make up the bulk material. Certain things can happen, but only over a limited distance. For example, in a non-conducting dielectric, the field does not strip the electrons and moves them about like it can in a conductor, but rather it stretches the atom into a dipole moment. The electrons bunch in the direction of the electric field leaving the nucleus to move away. This results in a small dipole moment. Since the bulk's dipole moments will follow the field, you get polarization within the dielectric.

The charge gets distributed throughout by the fact that it is restricted from moving about the bulk, unlike in a conductor.
 
  • #5
well ....yeah ..that makes sense......thanks.
 

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