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Understanding Electromagnetic Induction: Key Principles and Applications

Chapter 22 delves into the foundational concepts of electromagnetic induction, focusing on induced electromotive force (emf) and induced current. It explores how changing magnetic fields, coil area, and orientation affect current flow. Key principles include the separation of charges due to magnetic fields, Lenz’s law, and Faraday’s law. The chapter highlights applications such as microphones and guitar pickups, illustrating the practical relevance of these concepts in modern technology. By understanding these principles, readers can appreciate the interplay between magnetic fields and electric currents.

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Understanding Electromagnetic Induction: Key Principles and Applications

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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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