flatantsmu

2022-10-01

"The only power consumed in a DC electromagnet is due to the resistance of the windings, and is dissipated as heat."
Is this true? So powerful magnets like junkyard magnets don't consume electricity apart from resistance?
How much does electricity does a junkyard or any other powerful super magnet consume?

### Answer & Explanation

Collin Gilbert

Yes, in electrical circuits of only passive elements (Resistors, Capacitors, and Inductors) only the Resistors dissipate power (as heat). Active elements like transistors can also dissipate power, and if the currents in the circuit are changing with time, then power can be radiated away in electromagnetic waves. Therefore, the electrical resistance of the magnet coil dissipates power.
Additionally, power may be dissipated in the iron core of the electromagnet or in iron the magnet is picking up. As the DC current is turned on, a voltage is induced in the magnet's iron core by the changing magnetic flux. This causes power to be dissipated in the resistance of the iron. Likewise, as the magnet is brought near a piece of iron being picked up, the magnetic flux in the piece changes, a voltage is generated, and power is dissipated by the piece's resistance

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