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Chapter 22

Chapter 22. Electromagnetic Induction. 1) Induced emf and induced current. Changing B-field induces current. Changing coil area or orientation induces current. Changing the number of lines of force through loop induces current. Induced current indicates induced emf and induced electric field.

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Chapter 22

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  1. Chapter 22 Electromagnetic Induction

  2. 1) Induced emf and induced current • Changing B-field induces current

  3. Changing coil area or orientation induces current

  4. Changing the number of lines of force through loop induces current • Induced current indicates induced emf and induced electric field • Changing magnetic field produces electric field

  5. FB v + v - FB 2) Motional emf • The principle • B-field exerts force on moving charges

  6. E E ==> free charges separate • separated charges produce electric field and a corresponding potential difference

  7. E E FE + - FE • E - field exerts force on charges

  8. so, E E • Charges stop moving when the forces balance: Induced emf predicted from statics

  9. 2) Motional emf b) Application

  10. FB FA= FB c) Induced emf from conservation of energy

  11. Using, FB FA= FB Power to push rod at speed v:

  12. So, FB FA= FB Power to push rod at speed v: Electrical power consumed:

  13. B f Normal 3) Magnetic flux, F • Define Flux: - Proportional to the lines of force through a surface

  14. t b) Flux and motional emf

  15. 4) Lenz’s law Direction of induced current produces a magnetic field that opposes the change in flux • flux into loop increases because of v: DF/Dt > 0 • induced current produces flux out of loop (opposite direction) • Define external flux as positive. Then

  16. flux into loop decreases because of v: DF/Dt < 0 • induced current produces flux into loop (same direction to oppose the decrease) • Define external flux as positive. Then induced flux is also positive, so again v

  17. 5) Faraday’s Law For any changing flux in any loop, the emf induced in the loop is (for N turns) where F is the flux through one turn

  18. 7) Induction and sound • Microphone

  19. Guitar pickup

  20. Magnetic tape

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