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Can a block of aluminum become an electromagnet?

  1. Oct 31, 2011 #1
    So I have this huge solid cylinder of aluminum about a foot tall, and 2-3 inches in diameter. I understand that aluminum is not a permanent magnet. But it DOES conduct electricity. So, if I wrapped a conductor around it, and hooked that up to a power source, would the aluminum become an electromagnet? I'm guessing yes? How well of a magnet would it be compared to an equally sized cylinder of iron?

    Also, if so, what are some ways to increase the strength of the magnet? The idea is to wrap wire around it as many times as possible, I know that. But what about current and voltage? Will the strength increase if I increase either of those? I don't think I have much control over current, though. Using a thicker wire, would help too, decreasing resistance, right?

    This isn't going to induce a huge magnetic field right? I don't want to attract everything metal in the room toward myself.
  2. jcsd
  3. Oct 31, 2011 #2
    You can you aluminum but the result, as regards the B vector, will be poor (same as with air).
    An iron core would provide a higher B. The field amplitude grows with the current and the number of turns.
  4. Oct 31, 2011 #3
    So, you're saying it will produce no measurable magnet field? Isn't there some kind of table of values that show how certain materials react to an electric field?

    My idea is that since aluminum is an excellent conductor, electrons are able to easily flow through it. So wouldn't that mean electrons would move to one end of the aluminum when an electric field is induced around it, thus causing one end to be negative, and the other positive? That's how magnets work, right?
  5. Oct 31, 2011 #4
    He is saying you can but using something like iron will produce a stronger magnetic field.
  6. Oct 31, 2011 #5
    I think you are confused. A current through a wire wrapped into a coil will produce a magnetic field even with nothing at all in the middle, even a perfect vacuum. Adding aluminum in the middle won't increase it much, adding iron will. This has nothing to do with separation of negative and positive charges. Why do you think one end would become negative and the other end positive?
  7. Oct 31, 2011 #6
    Electrical conductivity and magnetic permeability have little to do with each other.

    The magnetic field you will get with an aluminum core will be the same as the field you get with no core (you don't need any core at all to have an electromagnet). The field you get with an iron core will be several times stronger.
  8. Oct 31, 2011 #7


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    Basically, a ferromagnet is a material that the magnetic moments of it's atoms tend to align easily with an external magnetic field, thereby increasing the strength of the magnetic field.

    We can find H, the magnetic inductance using Ampere's law for free currents. This H will be the same for no matter what material you use in the "core". It is simply given by the way you usually get the B-field of a solenoid. The B field is then: B=mu*H, where mu is the magnetic permeability of the material. If mu is very high (like for iron), then the magnetic field you produce due to both free and bound currents is very large. If mu~1 then there is no amplification effect.

    The mu for Aluminum is very very nearly 1 (wikipedia says 1.000022), so it would give you almost no amplification for your magnetic field created by the free current.

    Compare this with the mu for a mu-metal (an alloy designed to have high-mu), which has mu~20,000-50,000. This means that the magnetic field due to the free currents would be amplified 20-50 thousand times by using a core with a mu-metal (assuming at least you are in the linear regime)!
  9. Nov 1, 2011 #8
    Wow! You guys are like the eye doctor! I can see clearly now. Thanks for the thorough description. I guess my flaw was in understanding how magnets work. I actually didn't know permanent magnets and electromagnets are so similar. So, the atoms (or ions) in an aluminum core aren't free to move and align with a magnetic field created by the coiled wire. Too bad it's aluminum. Boy, would I have a lot of fun with an iron core of the same size.

    Physics is amazing!

    And by the way, there are a variety of symbols, including the greek letter mu, available on the right hand side when preparing your post.
  10. Nov 1, 2011 #9
    Actually there are some electrons in aluminum which are free to orient their magnetic momentum with the external field. This is a week effect though, called paramagnetism.
    To have the strong effect seen in iron (ferromagnetism) the magnetic momenta of the electrons must align with each other even in the absence of the external field.

    For a block of conductor you may see another effect, much stronger. If your external field is variable it will induce currents in the core. These currents will produce a magnetic field of their own. If your external field increases the induced field will be opposite to the external field. Overall, it will have a diamagnetic behavior.
    Counting the heat generated by the currents in the core too, I think you are better off without the aluminum in the coil of the electromagnet.
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