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Detecting induced electric fields in the ocean

  1. Jul 21, 2012 #1
    Hi everyone:

    Since there are many ions in ocean water, and these ions are carried by ocean currents, and they are moving through the earth's magnetic field, by the electromagnetic induction laws, wouldn't there be a induced electric field in the ocean?

    if i want to detect this electric field, would all i need be a piece of conducting wire connected to a very sensitive voltmeter and then place it in the ocean?

    p.s: couldnt this be used as a very sensitive tsunami detector? when a tsunami wave passes through, there would be an increase int the speed of conductors.
  2. jcsd
  3. Jul 21, 2012 #2


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    An interesting idea, but there are equal numbers of positive and negative ions in sea water, so any effects would cancel out.
  4. Jul 21, 2012 #3
    here is the composition of seawater according to wikipedia:

    Component Concentration (mol/kg)
    H2O 53.6
    Cl− 0.546
    Na+ 0.469
    Mg2+ 0.0528
    4 0.0282
    Ca2+ 0.0103
    K+ 0.0102
    CT 0.00206
    Br− 0.000844
    BT 0.000416
    Sr2+ 0.000091
    F− 0.000068

    from inspection, it can be seen that seawater has slightly more negative ions than positive.

    edit: more positive than negative, but only a small amount: .00227moles/kg
    Last edited: Jul 21, 2012
  5. Jul 21, 2012 #4


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    The main salt in sea water is Sodium Chloride which dissociates as follows:

    NaCl → Na + + Cl -

    giving equal numbers of positive and negative ions.

    The other salts do the same thing when they dissociate.

    There may be more Cl - ions because more than one Chloride formed the original salt mixture.

    The list doesn't give H + and OH - ions which would be considerable unless the seawater was completely neutral.
  6. Jul 21, 2012 #5


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    royzizzle, measuring fluid motions by monitoring the electric fields of ions in the fluid seems like a good idea. The charged particles do move through the earth’s magnetic field and, of course, they do obey induction laws. Using the basic laws of physics to create measuring devices is always a sure path to new and innovative ideas.

    As for a tsunami detector, this mechanism probably would not be viable. If the sensitive voltmeter was immersed in the ocean to measure fluid motion it may be difficult or impossible to discriminate between normal ocean waves and a passing tsunami wave. Here are a few excerpts from the Wiki tsunami page:

    “Tsunami waves do not resemble normal sea waves, because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide, and for this reason they are often referred to as tidal waves. Tsunamis generally consist of a series of waves with periods ranging from minutes to hours, arriving in a so-called "wave train".[4]

    Tsunamis have a small amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometers long, whereas normal ocean waves have a wavelength of only 30 or 40 metres),[22] which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 millimetres (12 in) above the normal sea surface. They grow in height when they reach shallower water, in a wave shoaling process described below. ”

    Now, it may be useful to read up on how tsunami warning systems are now being implemented around the world. Basically, they measure the increase in pressure caused by the passing tsunami wave using sensors on the sea bottom. See:

    Observation: Maybe your basic idea of measuring ionic motion would find useful applications in biomedicine where measuring blood and urine flows is important. And what about in neuroscience, where minute ionic charges are moving around our nervous systems and inside our brains? I hope you are keeping a notebook with your ideas.
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