# Homework Help: Force per unit length between two parallel whires of +/- X volts

1. May 29, 2012

### kryzlof

1. The problem statement, all variables and given/known data
Two parallel whires, separated by a distance D (midpoint distance), are charged with a current density L (each whire has a radius R). If the whires have the potential +/- X Volts, what is the force per unit length between them?

2. Relevant equations
B = μ0*I /(2πr) is describing the magnetic field at a distance r perpendicular from the whire.

F=B×IL is describing the force

3. The attempt at a solution
?

2. May 29, 2012

### MalachiK

The L in your second equation is the length of the wire, I think. Current density is the current per unit cross sectional area of the wire. It might be helpful to call this J or something so that you don't get confused.

It seems like a good idea would be to start off by getting an expression for the current in the wires. Your second equation can be rearranged to give the force per unit length in terms of the other quantities in the question.

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