200 likes | 339 Views
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.
E N D
Chapter 22 Electromagnetic Induction
1) Induced emf and induced current • Changing B-field induces current
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
FB v + v - FB 2) Motional emf • The principle • B-field exerts force on moving charges
E E ==> free charges separate • separated charges produce electric field and a corresponding potential difference
E E FE + - FE • E - field exerts force on charges
so, E E • Charges stop moving when the forces balance: Induced emf predicted from statics
2) Motional emf b) Application
FB FA= FB c) Induced emf from conservation of energy
Using, FB FA= FB Power to push rod at speed v:
So, FB FA= FB Power to push rod at speed v: Electrical power consumed:
B f Normal 3) Magnetic flux, F • Define Flux: - Proportional to the lines of force through a surface
t b) Flux and motional emf
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
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
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
7) Induction and sound • Microphone