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How do u make a variable electromagnet??
- yasmin (age 13)
One way is to include a variable resistor in series with the
electromagnet and battery. The power dissipated in a resistor is V*V/R,
where V is the voltage across it in volts and R is the resistance in
Ohms. In the steady state, the voltage across the electromagnet's
terminals should be very small (although this depends on how many turns
of wire it has and how thick the wire is). The power dissipated in the
resistor should be maybe a half a watt or so for a reasonable
flashlight battery in order to make it have a reasonable lifetime (less
power dissipated will make your battery last longer).
One drawback with that simple circuit is that most of the power
gets thrown away in the resistor. Another method would use a variable
transformer and an ac source to get a variable ac voltage. That can
then be converted to dc with a bridge made from four diodes, and this
variable dc can drive the electromagnet. The advantage is that there
are only minor power losses in the transformer and the diodes. However,
if you're starting with line voltages, you have to be very careful not
to get electrocuted. Low voltage batteries are very safe.
(republished on 08/02/06)
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