This might be a stupid question, but I can't find the answer anywhere. Why don't objects such as rings that people wear (which are made out of metal) have electric current in them? As far as I know all the requirements are met (magnetic field exists, electrons can freely move).

  • $\begingroup$ In an AC magnetic field there will be a current induced in a ring and one can measure a voltage between any two points along its surface (as long as there is an effective perpendicular field component), but for the kinds of magnetic fields we are exposed to it's usually not a problem. OTOH, putting a ring into a microwave or wearing one inside an MRI machine is not a good idea. $\endgroup$ – CuriousOne May 17 '16 at 19:57
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    $\begingroup$ A changing magnetic field induces a current. See Can the Earth's magnetic field be used to generate electricity? (possible duplicate) $\endgroup$ – pentane May 17 '16 at 20:08

A change of magnetic field induces a current, not the existence of the field itself.

That implies that if you move your metal ring around (like waving your hand) or change its orientation to the earth magnet field, a current will be induced; proportional to the change. When you stop moving, the current stops of course too.

What effect would you expect? If you do it a lot, the resistance of the ring will start to warm it up a bit. It needs a lot of moving to get any feelable effect though, as the earth's magnetic field is not very strong, so the current-inducing change and therefore the current are also not very high.

If you put an ampere-meter in the ring, you would be able to measure the current (but waving it around gets a lot more cumbersome, probably).

If you use a much stronger artificial magnetic field, make the ring larger, and move it around very quick, you will get a lot of current. That is called a Generator.


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