1. Electromagnetic Induction
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. 2) Motional emf The principle • B-field exerts force on moving chargesFB + v FB

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

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

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

9. 2) Motional emf
b) Application

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

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

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

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

14. 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