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Do you think, one could split a mercury drop into two drops with the magnetic force? Mercury is a liquid metal, hence if I put a current through it, it will become a electromagnet (a wire with a current induces a magnetic field).

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If I then place two magnets on each side, but sufficiently separated, I thought that the fluid "electromagnet" will split and both sides will travel to the magnets.

  • $\begingroup$ 1) Have you checked whether Hg is magnetic? 2) Have you considered that any metal can be liquid or solid depending on the temperature? $\endgroup$ Apr 8, 2017 at 13:10
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    $\begingroup$ @CarlWitthof, At room temperature, the element mercury is not very magnetic at all. It has a very small, negative magnetic susceptibility... but if I pass a current through it, the current will induce the hg to become magnetic. ... maybe it's wrong, but this is what I am assuming. $\endgroup$
    – henry
    Apr 8, 2017 at 13:26
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    $\begingroup$ I think you would need a changing magnetic field for that? $\endgroup$
    – peterh
    Apr 9, 2017 at 19:46
  • $\begingroup$ @peterh could you explain n more details ? $\endgroup$
    – henry
    Apr 9, 2017 at 20:34
  • $\begingroup$ I am not very good in this, but maybe this video could be interesting for you. $\endgroup$
    – peterh
    Apr 9, 2017 at 20:38

2 Answers 2


It looks like it should work. It is a little more geometry specific than you are thinking, so I have modified your design below.

It will require a reasonable amount of experimentation to perfect the correct permanent magnet strength, required current, and distances to match the surface tension of mercury, etc. Other things that would need to be tested include containing the mercury droplet and bringing the droplets back together when current is reversed (if necessary).

Mercury Drop Separating Apparatus

Diagram Notes:

  1. Green Arrows = Desired electromagnetic applied force
  2. Cyan Arrows = Surface tension force that must be overcome (just a generalization; it is much more complex than this)
  3. Yellow Arrows = Electric current (note that this is "hole current"; electrons move the opposite direction). Don't get too hung up on direction; you just reverse the polarity of the electrical current if you have it backwards.
  4. Purple Arrows = Magnetic field (out of and into the page respectively). Putting an iron back plate on these magnets will increase their strength. Leaving some gap between them will also increase their strength; this gap can be filled with any non-ferrous material.

Design Considerations:

  1. You will need to have long electrodes (as opposed to points in your drawing) so both droplets can stay in contact with the electrodes as they are pulled apart. If the current stops, so does the separating force.
  2. Surface tension is the force you are working against. Bringing the electrodes close together so the mercury droplet is squished will decrease the current required to separate it. If the droplet is not squished it may try to move the whole droplet one way or the other instead of separating it.
  3. You may need to experiment with different metals for the electrodes; some may have better "wetting" or angle of contact with the mercury droplet because of surface tension properties.
  4. The magnetic field through the center will not be into or out of the page, so electrical current in this area will not provide a force in the directions of concern. Possibly putting an insulator in this middle zone may improve the design.

HyperPhysics - Magnetic Force on a Current-Carrying Wire

  • $\begingroup$ Very nice - colorful as well! Is the externally applied magnetic field drawn somewhat similar to the field produced by the current, except much stronger? I'm having trouble imagining the shape in 3D. $\endgroup$
    – uhoh
    Apr 10, 2017 at 1:34
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    $\begingroup$ @uhoh, Its easiest to think of it in terms of an electric charge traveling through a magnetic field results in a 90 degree force. Have a look at the hyperphysics link at the bottom of my answer. A wire by itself produces a magnetic field, but you will hurt your head trying to visulize (or calculate) how the two magnetic fields will interact. $\endgroup$
    – ericnutsch
    Apr 10, 2017 at 1:51
  • $\begingroup$ I will endure the pain and read the link again. Thanks! $\endgroup$
    – uhoh
    Apr 10, 2017 at 2:42
  • $\begingroup$ Lol, The right hand rule for a charge moving through an electric field is just one of those laws of the universe you have to remember. It will match the result of looking at it as two magnetic fields, and is much easier to understand. This pdf link explains it several different ways: odu.edu/~jdudek/Phys112N_materials/4-magnets.pdf $\endgroup$
    – ericnutsch
    Apr 10, 2017 at 3:00
  • $\begingroup$ Wow !! This is perfect . Very nice illustration! Thanks a lot ! :) :) $\endgroup$
    – henry
    Apr 10, 2017 at 8:45

To add to Eric's Answer, you can see a visual demonstration from Physics Girl - this really does work with another magnetic liquid - Oxygen


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