1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

AC Coil Levitation

  1. Jan 23, 2015 #1
    Hi pf,

    I am trying to get a fun experiment for a science fair at school and would greatly appreciate some help. I have found the experiment I want to do in the video below (43mins 50seconds in). The school has a large aluminium plate so that is sorted. What I am having difficulty with is getting a coil to show appreciable levitation and without stopping it getting really hot (and even smoking). What kind of coil does the professor use so that it doesn't heat/smoke? Also, I am driving the ac with a school power pack which is why I don't think I am getting that much levitation. What device is he using in the lecture and are they easy to get hold of? Any help/guidance is much appreciated!

  2. jcsd
  3. Jan 24, 2015 #2
    I have no idea, sorry. But you'll need a material that has a high specific heat and low resistance, so that it doesn't heat up and the force is sufficient.
  4. Jan 24, 2015 #3


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    how many turns on the coil ?
    what is the physical size of your coil ?
    what voltage were you putting in to the coil ?
    what current was being drawn by the coil ?

  5. Jan 25, 2015 #4
  6. Jan 27, 2015 #5
    Sorry, I had no notification anyone replied to this thread. Thanks for the answers. The MIT professor looks like he is using mains insulated cable so this is what I tried (as I previously tried bare copper wire which just smokes). The mains cable I have tried is rated at 6A max. This seems to be the highest current rating I can find which has a similar diameter to the one used in the MIT video. I have tried winding it with 4 loops and 8 loops but with no joy for either. When you wind the cable into a loop you obviously have two ends (i.e. two sets of a live and a neutral). I plugged one live wire into 1 terminal of the a.c. on a school lab power pack and the other live into the other terminal. The wire (despite being insulated) got very hot but even on max output (16V) from the power pack no levitation! Our school has a big aluminium sheet (roughly 1m by 1m) which is what the cable rests on. I also tried plugging both neutrals into one terminal and both lives into the other hoping to get a voltage across them but this did nothing. It looks so simple in the video, a coil of wire, a metal plate and a supply of mains a.c. What am I doing wrong?
  7. Jan 28, 2015 #6
    If you can't increase frequency, than increase number of turns/loops of the wire in the coil while keeping same amperage flowing through it. Weight of loop rises proportionaly with number of turns but force rises faster. Also, think about using thinner wire , smaller max current, flat coil and thick aluminium plate.
  8. Jan 28, 2015 #7
    In the video, the wires coming from the power supply aren't all that thick, so the wires of the loops can't be much thicker. I'm guessing there are a few hundred loops of transformer wire with enamel isolation wrapped with some king of isolation blanket made of glass-fiber, so Levin's wires are also getting hot.
  9. Jan 29, 2015 #8
    Levin used at least 100 turns of relatively thin wire . This video shows experiments with awg 22 magnet wire:

    Note that for good results at 60 Hz, aluminium plate needed to be about 10 mm thick.
  10. Jan 29, 2015 #9
    Excellent, thanks guys. I will try this out over the next couple of days.
  11. Jan 29, 2015 #10
    And how about using an aluminium magnet wire for the coil? Aluminium is much lighter than copper.
  12. Feb 6, 2015 #11
    Right, I have got hold of 150m of copper magnet wire and wound it all up as per the video. The aluminium plate I have is at least as thick as the one in the video and still no joy! When I plug it into a school power pack it does buzz and hum so it definitely is trying to levitate. It must therefore be that I can't drive enough current through it. Does anyone know of a way/device to drive a large a.c. current?
  13. Feb 6, 2015 #12
    Probably, voltage of your school power pack is too low to drive enough current through the coil. You may want to use variac in such experiments. Make sure if the aluminium plate is really made of aluminium or it is just some alloy that looks like it (can make substantional difference). Also, try to get hold of aluminium magnet wire . You'll need less current to levitate it.
  14. Feb 6, 2015 #13
    Thanks for the reply. What is variac? In the video with MIT professor he actually says "I then just plug it straight into 110V mains ac". So he plugs it straight into the mains but he has some sort of intermediate device which varies the current (which looks like a black box in the video), what would this be?
  15. Feb 6, 2015 #14
    Variable autotransformer
    MIT professor can plug the coil straight into AC mains becouse he is professor :). You better don't..
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook