Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Maximum pull a of normal magnet

  1. Nov 10, 2004 #1
    What is the maximum pull a normal magnet (non electromagnet) of about the size of a computer mouse could achieve? And how would the cost of this compare to the cost of an electromagnet of the same pull? Also, will an electromagnet achieve it's desired pull immediately when the circuit is closed? Thanks.
  2. jcsd
  3. Nov 10, 2004 #2
    Hard to give exact figures, but I've just bought some incredibly strong Neodymium magnets to play with in the Lab. These are AWESOME! If you put a 2" x 3" magnet on a steel surface you can't lift it off!

    I bought 10 small 1" round magnets and one big one and when they are together I struggle (and I mean struggle!) to pull them apart. They also jump back together and can really hurt when they pinch your skin. When handling them, you have to hold them tight or they jump out of your hands if they are near another magnet.

    I'll see if I can measure the force needed to seperate them later this week.

    In the meantime - buy some on Ebay. I bought mine from this great Ebay store:
  4. Nov 13, 2004 #3
    If you need a strong magnet quick , dont bother with permanent magents. Electromagnets do get the full force just about immediatly
    (if you can wait the fraction of a second for hysteris).

    I used neodymium magnets myself, very extremely powerful, and potentially dangerious.

    If you are going to manufacture an electromagnet use iron or something as the core for the inductor. If you can get your hands on some finishing nails, then duct tape them into a role, and then wrap that with wire, it works wonders, just use a nine volt battery at either end of the wire terminals. Their you'll have a magnet stronger then any neodymium magnet you could buy.
  5. Nov 15, 2004 #4
    Do Not follow the last advice you may explode the batteries -- for some people there is no hope !
  6. Nov 18, 2004 #5
    Thanks guys.

    Is there a significant difference in the power of an electromagnet using AC current and one using DC current?

    How long would you guess a few D batteries or 9V or w/e would last that could power an electromagnet with a pull of about 100 pounds? I'm not sure if my question is answerable becuase I don't really know what I'm talking about.
  7. Nov 18, 2004 #6
    There is no basic reason for AC to be different from DC since AC can be as slow as you like -- however if the AC if fast then you must allow for a) the inductance of the winding which will reduce the current for a given input voltage and b) there are core losses due to hysteresis ( ie. heat produced in the core over and above any dc loss in the winding ). For normal house ac the effects are probably not large .
    In any event trying to produce strong electromagnets with house ac is a little dangerous, it would be adviseable to do a few simple calculations on resistance , power , etc to avoid fire hazards aside from the chance of shock -- this is also true of using NI Cads etc you should limit the currents to avoid battery heating ( suggest you contact a supplier for info on this ) I.e. Max allowable sustained current drain .
  8. Nov 18, 2004 #7
    If you have an old computer hard disk it has some really good magnets in it. (and i mean good as in you REALLY dont want to get your finger stuck between them ).
    If you cant find one though, making an electromagnet is quite easy, although a bit time consuming. I dont think it will be strong enough to pick up 100 pounds though
  9. Nov 23, 2004 #8
    Could anybody direct me to a site that explains a fair amount of technical details about how an electromagnet's pull, watt requirements, voltage, size, etc. all relate?

  10. Nov 23, 2004 #9
    Try 'Howstuffworks' as a start . Ray
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook