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Can moving ions in water produce a magnetic field

  1. Jun 16, 2010 #1
    I know that moving charges produce a magnetic field, my question is if a solution of water containing ions moving through a pipe or being spun would produce a noticeable magnetic field. Would current running through a solution of ions produce a magnetic field as well?

    Thanks in advance
  2. jcsd
  3. Jun 16, 2010 #2
    Yes, but you do need net (local) currents for this. Just letting salt water flow won't create amagnetic field. However, if you have a rotating conducting liquid, then you can get a so-called "dynamo effect" which gives rises toa magnetic field, http://farside.ph.utexas.edu/teaching/plasma/lectures/node62.html" [Broken]
    Last edited by a moderator: May 4, 2017
  4. Jun 16, 2010 #3
    with salt water there are positive and negative ions, does this cancel the field somehow, would a solution containing ions of only one charge produce a magnetic field? I don't understand how this doesn't work, is it that only moving electrons and protons produce magnetic fields so ions and charged molecules don't work?

    Thank you for your help.
  5. Jun 18, 2010 #4
    Any moving charged object will create a magnetic field, even some molecules have a magnetic moment, you have to remember that cations and anions in a salt solution are continuously moving due to thermal energy, however this motion is much like the thermal random motion of electrons in a conductor with no net current, the net field is canceled out.

    salt solutions are formed due to the decomposition of salt molecules into cations and anions, if you managed to remove cations by some electrochemical method it would be like a charged belt, moving it in one direction will create a magnetic field, however, the field generated will be very weak, the magnetic field density is directly proportional to the current intensity, here it comes to the charge to mass ratio m/q, which is very big for ions compared to electrons, it's about 3 orders of magnitude greater in ions than electrons.

    so you will need a huge amount of work to generate a detectable magnetic field that way.
  6. Jun 18, 2010 #5


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    Yes, it cancels, and yes it would, but charge would be extremely high.

    You want a very high number of charged particles moving to create significant magnetic field. That amount of charge simply cannot be contained if unbalanced. So normally, you observe magnetic fields when you have both kinds of charges, but manage to keep one moving and the other hold still, or make them move in opposite directions.

    Application of electric field works best. Drop two wires into a salt water, apply voltage, and it will create a magnetic field in it.
  7. Jun 18, 2010 #6
    I agree with the above posts.....any mobile charged particle will have an accompanying magnetic field.....electrons or charged molecules for example.

    " ions moving through a pipe or being spun would produce a noticeable magnetic field."

    It's there, but how "notcieable" or detectable it is remains an experimental issue, not a theoretical one. Within everyday experience, it would be tough to detect. A swift flowing river, for example, I doubt has much of a magnetic field associated with it...if it did, we could generate electric power really cheap!!! (Just hang a coil of wire nearby or in the river.)
  8. Jun 18, 2010 #7
    Thanks everyone, you all were very helpful
  9. Sep 10, 2010 #8
    Interesting thread,

    Suppose there is a way to place a long cathode and an long anode in the ocean and close to the shore where waves generate a substantial strong varying water flow. Both electrodes are placed in the direction of the water movement.

    Connecting them to a DC current source, the water will be ionized and the anions will go towards the cathode and an the cations toward the anode.

    Placing two coils, one around the cathode and one around the anode, each coils should pickup the magnetic field generated by the movement of the ions and theoretically convert it into electricity.

    I really wonder if this makes sense.
  10. Sep 10, 2010 #9
    Your using electricity to generate electricity? OK, but there will be losses such that it would have been better to just use the "first" electricity.
    Also, ion flow in a turbulent medium is, well, non-specific, and many ions might not be able to reach their target or be effectively influenced by it.
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