We have several magnetic stands on my university, see here. This stand has a button which makes you able to turn the magnet off and on. It is quite hard to press the button, it seems like something mechanical. But it must be a permanent magnet since it doesn't run on electricity, so I wondered, how is it possible to "turn off" a permanent magnet? Or am I missing something?


In reaction to CuriousOne:

If the button causes the magnet inside to move, than how does this work since the button seems to be one solid pin inside the stand, see the two images.

enter image description hereenter image description here


The mechanical button lowers or raises the magnet, which changes the effective force between it and the steel plate that the base attaches to. You are correct, one can not turn a permanent magnet off this way, but one can greatly change the force between it and a magnetic material by changing the distance.

After looking it up I have to correct myself. One particular design doesn't actually lower or raise the magnet but it turns a cylindrical magnet in an assembly between two magnetic jokes. This is a very important difference to my original suggestion, which would never completely eliminate the force between the magnet and the base plate. In the design shown in https://en.wikipedia.org/wiki/Magnetic_base it's the change in symmetry that can essentially completely cancel the field. It's quite ingenious, really.

  • $\begingroup$ That does make sense. But how does this button do this, since it seems to be one solid pin. Ive edited the question with some added images. Thank you for your response. $\endgroup$ – SjonTeflon Sep 11 '15 at 15:12
  • $\begingroup$ I can't tell you the detailed construction that's inside the black box. Mr. Screwdriver can, but he should only be used on property that belongs to you. Maybe you can get permission from the lab manager to open one of these things (there might be a broken one around)? It's worth a try and in a school setting curiosity is never embarrassing. $\endgroup$ – CuriousOne Sep 11 '15 at 15:15
  • $\begingroup$ Oh wow, so what it basically does is increasing the range by using iron blocks when it is on and decrease the range by using material which isn't ferric? That is pretty cool. $\endgroup$ – SjonTeflon Sep 11 '15 at 16:17
  • $\begingroup$ The rotation changes the symmetry of the magnetic field. In the off position the North and South poles of the cylindrical magnet are being "shorted" magnetically by the jokes and very little of the field extends to the base plate. In the on position one joke is magnetized by the North and one by the South pole of the rotated magnet, and the entire magnetic circuit is closed by the base plate. $\endgroup$ – CuriousOne Sep 11 '15 at 16:20
  • 2
    $\begingroup$ What are "jokes" in this context? $\endgroup$ – The Photon Sep 11 '15 at 16:59

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