Magnetic Fields

1. Magnetic Fields • Gauss’s Law vs. Ampere’s Law • Ampere’s Law • Ampere’s Law for long straight wire • Examples • Magnetic properties of materials • Force between 2 parallel wires • Motors • Loudspeakers

2. Magnetism and Induction Flowchart Current creates magnetic field

3. Gauss’s vs. Ampere’s Law • Gauss’s Law for closed surface • Flux lines penetrating closed surface equals charge enclosed. • Ampere’s Law for closed loop • Magnetic field integrated along closed loop equals current enclosed.

4. Ampere’s Law for long straight wire • Ampere’s Law • Symmetric loop around current I • Units • μo= 4π x 10-7T-m/A “permeability of free space” • Electric forms “spokes” magnetic forms “loops” • Electromagnetic field

5. Right hand rule II • Right hand rule for current carrying wire

6. Example 20-7 • Ampere’s Law for long wire • Direction: down into the page at point P

7. Example 20-8 • For B1 • For B2 • Total field (by inspection)

8. Example 20-9

9. Magnetism in materials • Spinning charge particle creates magnetic field • If all spinning particles align, you have a magnet

10. Force between parallel wires - 1 • Wire 1 sets up field. • Wire 2 feels force of that field. • And vice versa (wire 2 on 1) • F21=-F12by action-reaction

11. Force between parallel wires - 2 • currents same direction • currents opposite direction action-reaction pair

12. Magnetism and Induction Flowchart Wire 1 creates magnetic field Wire 2 feels force of that field

13. Example 20-10 • Field of first wire • Force felt on second wire

14. Example 20-11 • Field of first wire • Force on second wire

15. Problem 41

16. Problem 43

17. Problem 45

18. Rotating current loop • Force on each side of loop (fig a/b) • Left • Right • Moment arm of each torque (fig c) • Torque of both sides • For N loops of wire φ

19. DC motor • Current reverses every half turn • DC motor

20. DC Motor animation • DC motor animation • http://educypedia.karadimov.info/library/MccComplet.swf

21. Loudspeaker