# Balancing magnetic forces on rods

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1. Dec 29, 2015

### Will Freedic

1. The problem statement, all variables and given/known data
If two parallel rods are placed 1mm apart, with one directly above the other, each carrying a current I in opposite directions, of length L what is the mass of the upper rod as to balance the force

2. Relevant equations
F=ILxB

3. The attempt at a solution
I have little idea of how to go about attempting this solution, thankyou!

2. Dec 29, 2015

### Mister T

You need to assume the lower wire is held in a fixed position. It exerts a magnetic force $IL\times B$ on the upper wire.

3. Dec 29, 2015

### Will Freedic

Thankyou, but how do you work the magnetic field strength?

4. Dec 29, 2015

### cnh1995

Biot-Savart's law or Ampere's law will be useful here.

5. Dec 29, 2015

### Mister T

I suggest you look in a textbook. There should be a section on force between long parallel current-carrying wires.