# Magnetic field problem

1. Apr 5, 2005

### formulajoe

a three phase transmission line consists of three conductors that are supported at points A,B, c to form an equilateral triangle. At one instant, conductors A and B both carry a current of 75A while conductor C carries a return current of 150 A. Find the force per meter on conductor C at that instant.

heres what it looks like

A
|
|
|-------C
|
|
B

current at A and B is going in, current at C is coming out. Each point is 2 meters apart.

This is the z = 0 plane
im really stuck on this one.

2. Apr 5, 2005

### whozum

Where are you stuck, what have you tried?

Spit out some equations you think might fit.

3. Apr 5, 2005

### formulajoe

the only think i can think of is to find the H field about A and B with rho being equal to the distance to C. than use the int(i*dl cross B). do that at A and B ? i dont see how the 150 amp current causes a force at C.

4. Apr 5, 2005

### whozum

The force on a charge due to magnetic field from each wire will be:

$$F = i\int{B\times dl}$$

Now you'll want to find the force for wires A and B at point C. Does the current through C affect the magnetic field? How so?

5. Apr 5, 2005

### formulajoe

since the current at C is twice at the current at A and B than wouldnt that cancel out the magnetic field?