Homework Help: Magnetic Fields and Forces

1. Jun 7, 2012

skye204

1. The problem statement, all variables and given/known data
Two straight wire are suspended from the ceiling by strings length of 0.75m.
each wire has a mass of 45g and a length of 1m
When identical current flows in opposite directions, the angle between the string is 12°.

2. Relevant equations
Fg=mg
B=μI/2πR
F=LIBsin(theta)

3. The attempt at a solution
From the looks of it, I assumed that this was an equilibrium question meaning that the force of (BIL) is the same on both wires, working in opposite directions to create an angle of 12°.
I also assumed that the force of gravity (.441) is equal to the Y component of the string, so then i used trig to solve for the force of the X component which i found to be .0464.

The force of the X component is the same force as the (BIL) and in order for the forces to be the same, the magnetic field and current has to be the same.

so then i combined B=μI/2πR with F=LIBsin(theta) in order to cancel out the magnetic Field since it did not matter.

I got F= LμI2/2πR

I figured out the current to be 131.9

I would attach a picture of my work but i don't have 10 post..
imageshack.us/photo/my-images/265/photo20120607121104pm.jpg/
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution