# Magnetics question!

1. Dec 9, 2005

### Pseudo Statistic

A long piece of wire with a mass of 0.1kg and a total length of 4m is used to make a square coil with a side of 0.1m. The coil is hinged along a horizontal side, carries a 3.4A current, and is placed in a vertical magnetic field with a magnitude of 0.01T.
a) Determine the angle that the plane of the coil makes with the vertical when the coil is in equilibrium.

For this part I was thinking, mg = F = BILcos phi, where phi is the angle with respect to the vertical...
phi = arccos (mg/BIL)
Now, I thought, "Which L can I use?" and I couldn't find the answer using different values.. can anyone please show me where I went wrong?

b) Find the torque acting on t he coil due to the magnetic force at equilibrium.
I'm guessing a) will give me what I need for this part.

a) 3.97deg
b) 3.39 x 10^-3 Nm

Thanks for any pointers!

2. Dec 9, 2005

### Tide

Did you account for multiple turns of the wire? (total length is 4 meters but the perimeter of the square is only 0.4 meters)

3. Dec 9, 2005

### Pseudo Statistic

Isn't that only relevant to the torque?

4. Dec 9, 2005

### Tide

The current runs through each loop and the total current interacts with the applied field.