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I have to build a simple electric motor by attaching a magnet to a battery, extending the terminals of the battery (with stiff wires so they could act as supports), and placing a coil of wire on top of it. I know that the more loops you have in the coil the stronger the magnetic field and therefore the faster the coil will rotate. However, how does the diameter of the magnetic coil affect speed of the wire coil rotating? A smaller diameter might make the magnetic field stronger, but the magnetic force which produces torque would also be be applied closer to the center of rotation, therefore creating less torque.

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Assuming that the the wires are winded close together, than the magnetic field will be constant within the coil. –  fibonatic May 17 '13 at 12:06
So the diameter of the coils does not matter? –  Ovi May 17 '13 at 12:09
It will affect the resistance of the coil (which will reduce the current). –  fibonatic May 17 '13 at 12:36
Oh ok thank you –  Ovi May 18 '13 at 16:13

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