# U Electromagnet Optimization

I have a U shaped magnet (like the one we used to see in school, half red half blue) that I want to make out of it an electromagnet by winding around it a 0.5mm diameter insulated copper wire, covering it from end to end, with n layers ( n still being undetermined).

The goal is to rise some metal off the ground, the magnet being suspended over it in the air; once the circuit is running, the electromagnet’s field will get intense and be able to lift the weight, and once turned off again, the metal will fall back to its place due to its weight.

How would I get the best magnetic attraction out of that system? I’m working on it for a university project, so I want something to attract the judges with.

Any advice would be extremely welcomed.

• It's already a magnet. It might be the least useful thing to make an electromagnet of – find a non-magnetized piece of iron and do it with that? Commented Jun 10, 2018 at 19:58
• The material you use to make an electromagnet is not the same as the material you use to make a permanent magnet. Use a soft iron core instead. Commented Jun 10, 2018 at 19:58
• I added some info. Commented Jun 10, 2018 at 20:50
• Slice open a transformer to use it as laminated U magnet. Commented Jun 11, 2018 at 9:33

If you start with a U-shaped magnet, a permanent magnet, then what you have is a magnetically 'hard' material. Its permeability will be low, and it will have a retained magnetic field. In the second part of your demo, when you want to drop the things you've picked up, turning off the winding current will not do it, they will stay stuck.

If you pass current through windings on a permanent magnet, then it will slightly increase or slightly decrease the existing field. If you use some serious current, then you might be able to reduce the strength of the magnet permanently. This won't help you a lot, as you'd have to use just as much current to increase the strength again. This is how permanent magnets tend to be made. They are made unmagnetised, then magnetised with a huge pulse of current from a specialist power supply, a pulse to keep the power dissipation down.

You need a soft iron core for an electromagnet. This has high permeability, and will lose almost all of its magnetism when the current is off. A stack of Es from a dismantled Es and Is transformer makes a good magnet core.

The magnetic strength you'll get from any given electromagnet is $B\propto CopperMass \times \sqrt{power dissipation}$

That means, the more copper you use, the less power you need for any given field strength. It doesn't matter whether the wire is thick or thin, 1 or 10 layers. As long as it's wound in the right sort of region, then to first order, these are the only parameters that matter. So ideally, fill all of the winding space available. If you can't find that much copper, then you'll need to use more power than you would have done.