11-02-2014, 06:33 PM
(10-02-2014, 07:48 PM)John M0GLN Wrote: Its something I've puzzled about for years, if you have a bar magnet and revolve it in front of a coil as a simple dynamo, as the N pole approaches the coil a voltage will be induced, say a +V, then as it revolves further this V would reduce to zero and as the S pole approaches the V would go to -V, this would be an AC voltage, but what if instead of revolving 360° the magnet reverses direction after 90° back to its original starting point? The induced voltage will have risen from 0V to +V and back to 0V, if this was repeated wouldn't this just be a stream of DC pulses
Sorry, no it won't.
As the N pole approaches the coil you could well get a +ve voltage. As the magnet revolves further the voltage may well fall to zero. If you then reverse direction, the voltage won't rise again. You will instead get a negative voltage.
That's because the voltage depends not on the magnet's position, but on its velocity. Moving backwards reverses the voltage.
It's not possible to move a magnet cyclically and get a unidirectional voltage - you'll always get as much negative as positive.
