# Homework Help: How do you find the diameter of a wire

1. Feb 8, 2012

### angiep410

1. The problem statement, all variables and given/known data
I have a question where I'm given the voltage, mass, resistivity, and density of a wire and I need to find the diameter and the length. Can someone show me how to do both of these?

2. Relevant equations

I have no idea what equation would relate voltage, mass, resistivity, and density to the diameter and length.

2. Feb 8, 2012

### Instinctlol

Heres a hint. R=pL/A (p is rho). Find another equation to this and solve for the radius in A and times that by 2 which will give you your diameter

3. Feb 8, 2012

### angiep410

The actual question is:
A 17.00 Ω resistor is made from a coil of copper wire whose total mass is 37.0 g. The resistivity of Cu is 1.68×10-8 Ω · m and its mass density is 8.90×103 kg/m3. What is the diameter of the wire?

So would I use Ohm's law V=IR to find I?

4. Feb 8, 2012

### Instinctlol

Im not totally sure but, you are given the mass density (kg/m^3). If you can find a way to get a length out of that (meters), you can use the formula I gave you and solve for A.
A=4∏r^2, then solve for r and times that by 2

5. Feb 8, 2012

### angiep410

How should I get a length out of the density?

6. Feb 8, 2012

### Instinctlol

Try 1 m^4/ mass (kg) units will cancel out leaving you with m