1. Electro- magnetic Induction Lecture 3 AP Physics

2. Class Demo Producing a voltage with a magnetic field and a wire coil.

3. Result A voltage is produced by a changing magnetic field in a coil of wire emf We will call this voltage an emf (electro-motive-force) to remind us that it is induced by magnetism.

4. Faraday Michael Faraday (1791-1867) The experimentalist of 1800’s Invented motor, generator, transformer, electrolysis and the theory of electromagnetic induction

5. Magnetic Flux The voltage created depends on the magnetic field and the area

6. Magnetic Flux

7. Faraday’s Law of Induction The instantaneous induced emf equals the rate of change of the magnetic flux through the circuit

8. Lenz’s Law opposes The polarity of the induced emf is such that it produces a current whose magnetic field opposes the change in the magnetic flux.

9. Lenz’s Law

10. Example 200 turn square coil, 18 cm on a side had a resistance of 2 . Find the emf and current in the loop if the perpendicular magnetic field changes from 0 to 0.5 T in 0.8 sec.

11. Motional emf An emf will be produced any time there is relative motion between the circuit and the field.

13. Motional emf

14. Generators

15. The emf varies sinusoidally Depends on the number of loops, the magnetic field, the size of the loop and the angular velocity

16. Generators

17. The Motor A motor converts electrical energy to mechanical energy A generator converts mechanical energy to electrical energy

18. Eddy Currents Demo: falling magnet

19. Self Inductance

20. Self-inductance A coil will oppose any change in the magnetic flux. If there is a change, there will be an induced emf that will oppose the change. (Lenz’s Law) self- inductance This opposition to change is called the self- inductance of the circuit Self-inductance is like inertia: it opposes any change in the current. Applet: http://www.walter-fendt.de/ph14e/osccirc.htm http://www.walter-fendt.de/ph14e/osccirc.htm

21. Self-inductance

22. Unit of self-inductance is the Henry

23. Self-inductance For a solenoid, N turns and length l, the self inductance is

24. Energy Energy is stored in an inductor

25. Links Additional Links: http://www.physics.sjsu.edu/becker/physics51/induction.htm http://hyperphysics.phy-astr.gsu.edu/HBASE/magnetic/magcon.html#c1