# Calculate the electromotive force E

1. Dec 3, 2015

### bassi ali

hi,
How can I demonstrate the relationship of the electromotive force of a motor AC
thank you

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2. Dec 3, 2015

### cnh1995

Motional emf will be induced in the rotor. Use E=BLVsinθ*N (where v=rw and N=number of turns of rotor).

3. Dec 3, 2015

### cnh1995

For detailed demo, you can first prove the motional emf equation using Lorentz's force(F=BILsinθ) applied on electrons of a conductor and then apply the emf equation to this alternator.

4. Dec 3, 2015

### bassi ali

which force you talk about ???
the rectangle is fixed and the flow varies,
I think to use the flow of magnetic induction,
I think to use Faraday's relationship e = - dΦ / dt (the derivative currency flows on derivative temp).
in using Φ=∫∫ B.dS

5. Dec 3, 2015

### cnh1995

Then you should use Faraday's laws.
Right.

6. Dec 3, 2015

### bassi ali

but i find this expression : E = N L r w B cos(wt)
====> must find sin (wt) instead of cos (wt)

7. Dec 3, 2015

### cnh1995

Then you should assume the varying flux as a cosine wave.
sin(wt)=cos(π/2-wt).

8. Dec 5, 2015

### bassi ali

i have cos(wt) not sin(wt) !!

9. Dec 5, 2015

### cnh1995

Your varying flux function should be predefined, either sin or cos. If it is sin, emf will be in cos(wt).