1. Magnetic Fields in Wires

2. Strength of Magnetic Field Strength of the magnetic field produced by a current carrying wire is directly proportional to the amount of current Inversely proportional to distance from the wire (r) Varies by a constant  o /2   o – permeability of free space = 4  x 10 -7

3. Equation B = (  o /2  ) (I / r)

4. Example A vertical wire carries a current of 25 A up. What is the magnitude and direction of the field at a point 10cm to the right of the wire?

5. Forces Between 2 Wires Since wires produce magnetic fields when a current is applied, two current carrying wires will either attract or repel

7. Current In Same Direction Wires attract

8. Currents in Opposite Directions Wires repel

9. Forces Between Wires F/ l = (  o /2  ) ( I 1 I 2 / L) l – length of wires L – distance between wires

10. Example Two wires of a 2.0 m long appliance cord are 3.0mm apart and carry a current of 8.0A. What is the force between the wires?

11. Example A horizontal wire carries a current of 80A. A second wire 20cm below it must carry a current I 2 so that it doesn’t fall due to gravity, what is this current? The lower wire has a mass of.12g per meter.