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enter image description here

In the image above, we have the principle of induction cooking. An alternating current is run through the coil, which causes a change in flux. This change in flux induces eddy currents in the conductive pan, and by Joule heating/resistive heating (P=VI), this causes the pan to heat up.

So the only thing that you need is a pan that can conduct electricity/the eddy currents right? As long as the pan does not have a too low or a too high resistance.

However, why is the effect specifically optimal for ferromagnetic materials/conductors? How does the ability to magnetize somehow enhance the effect of induction heating? Does the magnetization of the pan itself somehow enhance the eddy currents or something?

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    $\begingroup$ This is something you can simply look up on your own. See: en.wikipedia.org/wiki/…. $\endgroup$
    – Bob D
    Commented May 3, 2023 at 21:08
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    $\begingroup$ I don't get what they mean with 'the iron concentrates the current', what physical phenomenon causes the current to get 'concentrated'? by the magnetization and why? $\endgroup$
    – Stallmp
    Commented May 3, 2023 at 21:11
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    $\begingroup$ @Stallmp - why is an iron core used in a transformer. (Well, not iron any more, but magnetic metallic glasses.) $\endgroup$
    – Jon Custer
    Commented May 3, 2023 at 22:21
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    $\begingroup$ It actually doesn't need to be ferromagnetic, it just need to have a high magnetic permeability. It just happens to be that ferromagnetic materials tend to have high magnetic permeability. Is there a reason for it ? $\endgroup$
    – Puck
    Commented May 4, 2023 at 7:19

1 Answer 1

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Ferromagnetic material is needed for the same reason that transformers working with low frequency alternating current (a.c.) need iron cores. The magnetic field generated by coils in the cooker's hob are supplemented by magnetic fields due to alignment by this field of magnetic domains in the iron. The resulting magnetic flux density may be hundreds of times larger than if there were no iron. Thus as the field changes, because it is a.c. that is passed through the coils, the changes are far greater than if there were no iron, and a much larger voltage is generated. Hence the heating effect is greater, despite the greater resistivity of the iron compared with that of (say) copper or aluminium.

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    $\begingroup$ Thanks! So basically the magnetization of the iron itself adds to the total flux, so you have an additional self inductance term? Is it correct to say that emf = -LdI/dt - MdI/dt? $\endgroup$
    – Stallmp
    Commented May 4, 2023 at 4:50
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    $\begingroup$ Yes, you'll have a self-inductance term, since you can treat the saucepan base as the (loaded) secondary of a transformer. $\endgroup$
    – Philip Wood
    Commented May 4, 2023 at 9:45
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    $\begingroup$ +1 I was at first skeptical about this answer, but the magnetic susceptibility of iron is indeed huge. Another point to check is whether the magnetization of iron can be reversed so quickly. $\endgroup$
    – Roger V.
    Commented May 4, 2023 at 12:19
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    $\begingroup$ @RogerVadim Just a gut feeling: in transformers you try not to use iron for high frequency because the hysteretic losses worsen the efficiency of the thing. Here you don't care if some power is "lost" because the magnetic domains can't readily follow the fields variations: you simply get more losses, i.e. more heat, which is what you are looking for anyway. $\endgroup$
    – LorenzoDonati4Ukraine-OnStrike
    Commented May 4, 2023 at 14:03
  • $\begingroup$ "Another point to check is whether the magnetization of iron can be reversed so quickly." I believe that induction hobs work at around 30 kHz. An internet source suggests that at this frequency the effective relative permeability of low carbon steel has roughly halved from the dc limit. If this is applicable it would not be problematic, but my 'facts' do need checking. $\endgroup$
    – Philip Wood
    Commented May 4, 2023 at 14:11

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