Do eddy currents only exist when the conductors are of a ferrous material?

Posted on August 29, 2011 by admin 1

In the wikipedia page for induction cookers it specifies that "cookware must be made of ferrous materials." As this is involves the production of eddy currents, do eddy currents only exist in ferrous materials.

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1 response to Do eddy currents only exist when the conductors are of a ferrous material?

  1. Biofreak
    August 31, 2011 at 03:15

    Wow, this took me awhile to figure out, since so many websites give incorrect information on this topic. But I think I got it.

    Eddy currents have nothing whatsoever to do with ferrous materials. Eddy currents are a feature of conductors in general. So any object that can conduct electricity can have eddy currents (and will) when subjected to changing magnetic or electric fields. That means that any metal should work in an induction oven.

    Now the issue I had was trying to figure out why the wiki article claims only ferrous materials will work for your pots. Here's what I came up with:

    Eddy currents are not the primary cause of heating in an induction cooker. Though eddy currents will cause heat, they only partially counter the change in magnetic field, which means most of that potential energy does not get absorbed by the pot.

    If, however, you use a magnetic pot (iron), then not only do you get an eddy current effect, but you also get an effect from the magnetic boundaries in the pot aligning with the external changing magnetic field. In fact, in a real-world induction cooker, this is the dominant heating mechanism. So if you use a magnetic pot, your pot will heat much faster and cook better than if it were simply a conductor.

    Now, I also want to bring to your attention that 'ferrous' is not the right term. What you want is a magnetic pot. Ferrous means iron containing. Now iron happens to be magnetic and is the most common magnetic pot, but nickel would also work because it is magnetic and not ferrous. Furthermore, stainless steal is a very common pot material, and includes a lot of iron, so is ferrous; but most stainless steal is not strongly magnetic, so it may not be a good pot for induction cooking.

    Looking over that wiki article, I think this is an excellent example of why wikipedia pages should not be used as a source… they are often wrong.

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