1. Interaction of Magnetic Fields
Suppose a current carrying wire is placed inside a horseshoe magnet as shown.

2. Suppose that the electron flow is into the page, away from us, which way is the magnetic field?

3. Suppose that the electron flow is into the page, away from us, which way is the magnetic field?

4. Let’s rotate the wire so that we can see the field lines better.
Above the wire, the magnetic fields combine together, below it, they cancel out. This results in a downward force on the wire.
Note: If the electron flow is reversed, the force will be upward.

5. Right Hand Rule:
Place your pointer finger (index) in the direction of the magnetic field.
Place your center finger in the direction of the electron flow.
Your thumb will point in the direction of the force.

6. Right Hand Rule:

7. The field strength is represented by B
The field strength is represented by B. The force a wire experiences is dependent on the field strength (B), the current in the wire (I), and the length of wire that is actually in the field. (l)
I.e. F = BI l

8. A power line is 95 m long and carries 120 A of current
A power line is 95 m long and carries 120 A of current. If the Earth's magnetic field is 5.0 x 10-5 T, what force is applied to the wire?
F = BI l
= 5.0 x10-5 x 120 x 95
= 5.7 x 10-1 N

9. Note that the wire must be  to the magnetic field
Note that the wire must be  to the magnetic field. If it is not, you calculate only the  component of the force.