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# Number of poles and induced voltage?

## Number of poles and induced voltage?

(OP)
Hello guys,
I get that turning a loop of wire across a pair of magnetic poles induces a magnetic field. But I don't really understand how frequency plays a role in this.
I've read a bit and saw that frequency is directly proportional to induced voltage and that it is not simply RPM but also related to Number of poles. So does that mean if you are rotating a loop of wire at a fixed speed(RPM) but you double the Number of poles(pairs of poles) it will result in a nearly doubled induced voltage?
So a output voltage of 1mV @ 2 pairs of pole and 100RPM will be 2mV @ 4 pairs of poles and 100RPM and so on and forth for the given loop of wire?
Is their a limitation to this?
Sorry if this elementary, my understanding of power generation is shaky at best.

### RE: Number of poles and induced voltage?

N Kim the device you describe is essentially a magneto. The output voltage is a function of how fast the magnet passes the coil (the wire in your example). The frequency is how fast the wire comes around to pass the magnet again.
• Increasing the number of poles will not increase the output voltage.
• Increasing the velocity the wire and magnet pass each other will increase the voltage.
• Increasing the number of turns in the coil (on a pole) will increase the voltage.
A short video Physics - Principle of an Electric Motor - Physics

CH 10 and 11 have a good explanation.
Young, Arthur Primrose. The Elements of Electro-technics. United Kingdom, Sir I. Pitman & sons, Limited, 1920.
This is a case where an old book has a very readable explanation.

### RE: Number of poles and induced voltage?

(OP)
Interesting! then whys is it that electrical engineers define emf as
= 4.44*Ø*f*z
where frequency is a function of both number of poles and RPM in the formula
f=(P*N)/120
where P is number of poles and N is the velocity in Rotations per minute

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