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Finding strength, pull, telsa (anything) of an electromagnet

  1. May 12, 2013 #1
    I have built a new electromagnet, my second one so far, in an attempt to make it better. I am trying to find its strength, whether that be in tesla, holding force (kg) or whatever other units there are, just so I can compare it with other magnets.

    What I have is a steel bolt wrapped with 1000+ turns of 26AWG copper wire. There are 8 AA batteries in series, giving about 12V, and a current of about 0.22A. The coil is approximately 7cm long, and has an outer diameter of approximately 1.2cm (I think the bolt is 3/8 of an inch), with 8 layers of wire.

    Can someone please provide me with the formula(e) required to find what I am looking for.
    If there are any other variables needed please let me know. Also, what are good alternatives for a bunch of AA batteries? I would like it to be portable - not connected to a powerpoint - and to have it more powerful, so more current from the batteries.

    Thanks for any help.
  2. jcsd
  3. May 12, 2013 #2


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  4. May 13, 2013 #3
    I looked at the formulae on Wikipedia, but I'm not sure which one is applicable. I only contact an object with one pole of the magnet, the head of the bolt.

    When it is talking about air gaps in the magnetic field path, is that talking about between the magnet, is it meaning the air gap between the magnet and the metal object? If so, then when the object is contacting it, the gap would be so close to zero that it wouldn't matter, would it?

    What I am looking for is the strength, as in holding force, of my magnet, when contacting the end of the steel bolt, wrapped in the coil. And also, if anyone has any ideas for a good, yet small power source.
  5. May 13, 2013 #4


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    The lifting capacity of an electromagnet is measured in Newtons.
    Here are a few factors that have an impact on the lifting capacity:

    Surface conditions
    Magnetic lines of force pass easily through iron, but not air. Therefore anything that creates space or an air gap (e.g. dirt, paper, moisture, burrs, rust or paint) between the magnet and the lifted object will have a negative impact on the lifting capacity of the magnet.

    Material to be lifted
    Steel with a high carbon content, such as St37, is nearly as good a conductor as iron. Alloys, however, contain non-magnetic materials that have a negative impact on the magnetic conductance. AISI304, for instance, is nearly as poor a conductor of lines of force as air.

    Thickness of load to be lifted
    The greater the number of lines of force that can ‘flow’ from the magnet through the load, the more effective the magnet field will be. If the load is thin, the material will become ‘saturated’ with lines of force, preventing some of the lines of force produced by the magnet from ‘flowing’ through the material.
    Magnet contact surface on lifted load

    If the entire magnet surface does not make contact with the load during lifting, the lifting capacity will be reduced.

    You may get more information here: http://instruct.tri-c.edu/fgram/web/mdipole.htm [Broken]
    Last edited by a moderator: May 6, 2017
  6. May 13, 2013 #5
    Thankyou for the response. I will attempt to wrap my head around what it is saying, I don't know how I'll go, probably badly.

    I'll get back to you with how I go...
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