Magnetic Induction

1. Magnetic Induction Transforming energy with magnetism

2. F = qv  B Lorentz Force Reminder Source: Griffith, The Physics of Everyday Phenomena Fis directed out of the screen.

3. CPS Question What is the direction of the Lorentz force on the charges moving in this wire? B A. D. B. E. C. F. I

4. + – induced potential Moving Creates a Potential B v

5. Motional emf • Moving a conductor through a magnetic field causes separation of charges. • Back-emf (motional emf) in conductor cancels potential from motion e = lvB • when l, v, B all orthogonal

6. V V Rotating Loop Creates Circuit B

7. Rotating Loop Creates Circuit B V V

8. a b c d e Group Work • At which position(s) does the most magnetic flux pass through the loop? • At which position(s) does the magnetic flux through the loop change the fastest?

9. a b c d e Group Work • What is the current direction at these points?

10. a b c d e Faraday’s Law • Greatest fluxF when perpendicular • Fastest change in flux DF/Dt when parallel

11. Motion V through the field v V induces a potential v B Rotation Powers a Generator which generates a current that charges the battery

12. changing field e e opposing field B needed I Lenz’s Law Explains Generator

13. Current in a Field Feels a Force B F I

14. Loop in a Field Has Torque B I I

15. current I I force F I B Torque Turns a Motor

16. Group Work Which direction is the flux change? What current would oppose it? What is the Lorentz force on each side? If the magnetic field intensifies, in what direction will the induced current be? B

17. Flux inside loop becomes more How a Microphone Works microphone geophone

18. How a Loudspeaker Works loudspeaker induced motion of magnet current-generated field attracts or repels magnet current

19. B m I Back Potential • As the motor turns, back-potentialDFB/Dt opposesm • Faster rotation  more back potential