# X-rays and transformer coils.

## Main Question or Discussion Point

The EM field of a magnet or electromagnet can be converted to electricity with the use of a transformer (coil). My question is... Does that hold up for the whole EM spectrum... IR through Gamma?

## Answers and Replies

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mfb
Mentor
You cannot convert "the field of a magnet/electromagnet to electricity" - in the way that afterwards the field would be gone.
You can harvest energy from moving magnets, slowing them down in the process. Simple setups will give you alternating current, where the frequency is proportional to the (rotational) velocity of your moving objects, with a prefactor given by the setup itself.
Rotations in useful setups are limited to ~10000 rotations per second, so you will not get any MHz-frequency from generators. And even that is far away from the frequency of infrared or even gamma radiation.

Ok, I thought that I once saw a prof use a tesla coil, and a flourecent bulb to show that em fields were all around. Maybe I was mistaken.

mfb
Mentor
Ok, I thought that I once saw a prof use a tesla coil, and a flourecent bulb to show that em fields were all around. Maybe I was mistaken.
That is similar to a transformator - you use alternating current to generate an alternating field, and this can be used to light lamps.

What rimmini seems to have been asking about is an antenna, or at least an antenna that takes the form of a coil. It takes some somewhat involved math to theoretically describe.

Small antennas have been made that are efficient at absorbing visible light, although they don't look exactly like coils.

Last edited:
sophiecentaur
Science Advisor
Gold Member
For direct interaction, as with a radio antenna, the antenna would need to be a couple of hundred nanometers long - molecule sized. But the photon energy would make the situation different from what goes on in a wire antenna at RF.