# What is exactly is a non-conducting material ?

1. Jun 15, 2011

### flyingpig

What is exactly is a "non-conducting material"?

1. The problem statement, all variables and given/known data

In many Gauss's law problems, we are often presented with "consider a nonconducting sphere with radius..."

I realize most of the time we aer suppose to assume it is an inductor, how are we to know it is NOT an semi-conductor?

How does Gauss's Law apply to a semi-conductor? Are wires in circuits semi-conductors?

2. Jun 15, 2011

### zhermes

Re: What is exactly is a "non-conducting material"?

A non-conducting material is an insulator (not an 'inductor'), in which the charges are frozen in-place (i.e. immobile).

You know its not a semiconductor, because it says its an insulator.

Application of gauss' law to a semi-conductor would be basically the same, but it would depend somewhat on the particular situation, and whether or not its a statics problem (vs. dynamics).

Wires in circuits are conductors.

3. Jun 15, 2011

### chrisbaird

Re: What is exactly is a "non-conducting material"?

A non-conducting material is one that does not have electrons in the conduction band ("free" electrons) and therefore does not readily carry a current. Another word for these materials is "insulator". Semi-conducting materials are essentially non-conducting unless doped or acted on in a way specifically intended to make them conducting. I would think that unless the problem specifically mentions doped semiconductors, you can safely assume they are not involved. Wires in circuits are regular conductors. It is the solid state transistors, diodes, etc. that are made out of semiconducting materials, but they are special cases that are coaxed to be conducting through doping.