Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Touching both terminals of a battery

  1. Feb 9, 2010 #1
    Sorry if this is the wrong forum. When I just touch any part of the metal of both terminals on a 9V battery with a multimeters probes the meter displays the voltage (although it said 20V not 9V for some reason). What I'm wondering is why people don't get electric shocks from touching both terminals of a battery at once. Wouldn't you be completing the circuit?
  2. jcsd
  3. Feb 9, 2010 #2
    Try touching it to your tongue.
  4. Feb 9, 2010 #3
    If you have an old analog meter with a special switch for reading ac volts (e.g. like the Simpson model 260 or the Triplet meter), you do get 2x the actual voltage. The analog meter should be on dc volts for reading batteries. Your skin resistance protects you from shock, up to a limit.

    Bob S
  5. Feb 10, 2010 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Electrical shock is due to current flowing through your body, not so much an electric field (voltage). The resistance of your skin and body allows you to obtain the current by ohm's law (although ohm's law is not strictly valid for a human body, in de sense that the resistance is not independent of the voltage). For a dry skin, this resistance is in the order of tens of KOhm.
    You start getting problems with currents from a few mA onwards, which means that you need several tens of volts before things get "shocky".

    With a wet or immersed body the resistance lowers and there the limit of "dangerous" voltage is lower (hence the example of the tongue).

    See for instance http://hyperphysics.phy-astr.gsu.edu/hbase/electric/shock.html
    as a starting point.
  6. Feb 10, 2010 #5
    Ah right that explains it I bought a "household meter" so its probably build for AC.
  7. Feb 10, 2010 #6
    Thanks. I didn't know skin had such high resistance.
  8. Feb 10, 2010 #7
    Current gives you the shocks, not voltage. But voltage vill intensify it as it increases.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook