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Measuring voltage between your fingers

  1. Aug 5, 2012 #1
    If I hold one lead of my multimeter to my left index finger, and the other lead to the right index finger, it gives a reading of around 30mV. The reading quickly drops when I leave it there. I tried measuring the voltage between myself and the ground and it read 0mV. Whats stranger is that if I hold the positive lead to my left finger, and the negative lead to my right finger, it gives me a negative reading and vice versa. Its like my left hand is a positive battery terminal and my right hand, a negative terminal. Whats going on here?

    I tried dipping my fingers in salt water but that didn't affect the reading. I measured the voltage between my tongue and finger and it gave a lower reading (around 20mV). Measuring between my thumbs gives a higher voltage (around 40mV). Like I said, the voltage starts dropping when I hold it there so the only theory I have right now is that theres negative charge building up in my right arm or hand and then when I apply the voltage to the multimeter. Any idea what the cause of this is? Also, can you try this yourself and tell me whether its the same for you or its just me. I had an operation on my right hand a few years ago and now my right hand gets less blood flow than the left one.
     
  2. jcsd
  3. Aug 5, 2012 #2
    There are electrochemical reactions taking place between the leads and your skin.
    That doesn't mean that there really is a voltage between your arms. Well there actually is a voltage that is produced by contracting muscles. Used for ECG. But you can't really measure that with a normal multimeter.
     
  4. Aug 5, 2012 #3
    Why do these electrochemical reactions produce a voltage though? Wouldn't electrochemical reactions like that be equal at both areas of contact and thus, produce no overall electrical potential between the two leads? This doesn't explain why the negative charge seems to be in my right hand either. The readings do fluctuate massively for some reason and change throughout the day. Right now the maximum reading I'm getting is 5mV. If I hold the terminals there, they seem to equilibrate at around 2mV. Electrochemical reactions between my skin and the leads can't account for this, I'm more inclined to suspect it has something to do with the blood and/or muscles but you say muscle related voltage can't be detected by a multimeter so it must be something else.
     
  5. Aug 6, 2012 #4

    NascentOxygen

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    Staff: Mentor

    I like a questioning mind. :smile:

    Different salt concentrations on your skin; different salts, even, resulting in different
    electrochemical half cells. Slightly different metals, different oxide layers. It´s possible, too, that there is an ohmic asymmetry — slight rectifying effect — at some of the metal/metal salt/metal oxide interface, and this could be rectifying a portion of the everpresent mains hum that exists on your body.
     
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