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Effect of Magnetic Fields in Water?

  1. May 10, 2009 #1


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    I'm interested in doing a project that involves submerging a very strong if not supercooled electromagnet in water; i'm concerned about the effect of the EM field on the water itself.
    I know a bit about Magneto Hydro Dynamics but i don't have the math skills to understand it entirely. college freshman and all.
    I understand that when you insert a magnetic field of a certain form (involving charged plates etc...) into water with current running through both the plates and the water, the water will follow the field lines; is this correct?

    So my questions:
    1. Does the EM field from an insulated EM coil interact with water alone (no current passing through it)?
    2. Does the EM field from an insulated EM coil interact with water which has a current running through it?

    Answers do not need to go incredibly deep into MHD because what i'm doing does not deal directly with MHD. I'm concerned about the possible side effects it may generate.

  2. jcsd
  3. May 11, 2009 #2
    What's a supercooled electromagnet?
  4. May 11, 2009 #3


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    The magnetic field won't have any effect on the water but if the magnet is "supercool" it might freeze it.

    The effect you describe is easy to do with Neodymium magnets.
    You have to have water with salt in it so that it conducts.

    You then get the motor effect where you have a current moving in a magnetic field and this produces movement in the water. The water is just like the wire in a magnetic field.

    It can be done with a Petrie dish and magnets above and below it. Probes in the water provide the electric current and movement of the water is seen by the turbulence in the water.

    Fleming's Left Hand Rule predicts the direction of water flow.

    But without electric currents in the water you won't see any effect.
    Last edited: May 11, 2009
  5. May 11, 2009 #4


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    Ok, Thanks vk6kro.
    Phrak- a 'supercooled' magnet is a magnetic superconductor. it is commonly chilled to temperatures as low as that of liquid nitrogen or liquid Helium. The advantage is that when they are superconductors (super cold) the level of resistance drops dramatically, allowing an enormous amount of power to flow through the wires which would normally cause the wire to melt or vaporize. the supercooled magnet still generates heat, but it is often minuscule. Google 'super conducting magnets'. they are often used in particle accelerators.

  6. May 11, 2009 #5

    Pure water is diamagnetic. It generates a field that opposes the applied magnetic field. It's substancially weaker than the usual forces associated with ferromagnetic materials by a few orders of magnitude.
  7. May 11, 2009 #6


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    Diamagnetic is a new term for me, so let me get this straight:

    if I had an insulated super cooled electromagnetic coil submerged in pure liquid water, the magnetic field would push the water away from the magnet? that doesn't make sense.
    What about salt-water?

    The ends of the coil are where it gets interesting it seems. Would the water displace itself there because of the extreme repulsive force of the magnet and the diamagnetic water?
    I'm probably wrong, but straighten me out.
  8. May 11, 2009 #7
    Diamagnetism is very weak. It may be disappointing in its weakness. It occurs with a static magnetic field. Adding salt wouldn't change the effect much, that I know of. But salt water, as a conductor, will develop an opposing magnetic field to a changing magnetic field. The salt water acts as though it is a shorted one-turn secondary of a transformer (because it is). This is the same thing as the usual classroom demonstration of a copper ring that is repelled from the end of a high frequency solenoid. Look up Lenz's Law.

    If you're interested, google 'diamagnetism'. All in all, there are 4 sorts of magnetic materials: ferromagnetic, diamagnetic, paramagnetic, and one other effect I forget.
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