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Q & A: choke dissipation

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Most recent answer: 10/22/2007
Q:
There is so much heat produced in a choke, but still we say power consumed is ZERO. Why?
- Sunny (age 17)
India(Delhi)
A:
Good question.

In an IDEAL choke, with no electrical resistance, there is no power consumed, if we also ignore the electromagnetic radiation. The reason is that the voltage and the current are 90 degrees out of phase. Energy flows in and out of the magnetic field on each voltage cycle, but the net power loss is zero. Some devices actually use superconducting coils, so they can come very close to this ideal.

Most real devices uses ordinary wires, often with some magnetic material inside the coil. The current flowing back an forth in the wires heats them up because they have electrical resistance, so there's some voltage in-phase with the current. The magnetic material also usually heats up a little because its magnetic domains can't quite keep up with the changing magnetic fields. That again produces a voltage in-phase with the current.

So what you've noticed is the difference between ideal devices and real ones.

Mike W.

(published on 10/22/2007)

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