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Measureing potential of ions

  1. Nov 22, 2012 #1
    Hi,What is a physical principle of measuring potential on membrane?
    Or on body,if you measure potential of heart.I know,it sounds,like my question is nonsense.But I know,that voltmeter measure potential through free electrons.But for example if I have two clamp on body(eintohoven triangle),we measure potential,which produce heart,but this potential has ion character.And ions doesn t go through electrode to voltmeter.So,how is it possible,that we get a potential.Ions go through wire to voltmeter?????

    I know,current is flow of particles with charge.But I have studied principle of voltmeter,and if I have understand it correct then if I want to measure potential we have to have flow of current to get result.I know,that potential is between two points and so,but still,if we need to measure potential we must have current flow too.And ions doesn t go like free electrons
    Thanks for clarifying....
     
  2. jcsd
  3. Nov 22, 2012 #2

    Simon Bridge

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    You know how a voltmeter works? You only need a very small current.
    http://en.wikipedia.org/wiki/Voltmeter

    It follows that if you are measuring a potential difference with a voltmeter then there are charges flowing ... for a standard voltmeter the charge carriers will be electrons.

    The voltmeter leads have lots of electrons which may respond to external electric fields.
    The skin (or whatever) will have charges as well, which the electrons will respond to. Ions with a deficit of electrons will accept them and those with a surplus will donate them - none of the ions need flow through the wires themselves.
     
  4. Nov 22, 2012 #3
    So,redox reactions are taking place during for example making ECG????
     
  5. Nov 22, 2012 #4

    Simon Bridge

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    Well - the voltmeter wires are weakly connecting two solutions with different mixtures of ions. What normally happens in that situation?
     
  6. Nov 22, 2012 #5
    So,am I right?Galvanic cell?
     
  7. Nov 22, 2012 #6

    Simon Bridge

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    Depends entirely upon the particular system being measured.

    Note:
    * usually putting multimeter probes on your skin gives zero volts.
    * when there is a "voltage measurement" you have to be careful about what is actually being measured and where.

    what I have answered is how there can be a reading on the voltmeter without having exotic ions travelling up the leads.
    Perhaps you can provide a specific example of what is puzzling you - stated more clearly?
     
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