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High voltage, low amps, why is this not fatal?

rjosh33

Full Member
7+ Year Member
Jul 28, 2011
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  1. Medical Student
    What is the discrepency between amps and voltage??

    Voltage is the electrical potential. It is measured in volts, of course, which are joules per coulomb (J/C). So it is a measure of the energy per unit of charge.

    Amps is the unit for the current that is actually running through an electrical circuit. Its constituent units are coulombs per second (C/s), so it is a measure of the rate at which charge is flowing. A high amperage (current) means a lot of charge running through the circuit that is carrying a certain amount of energy (how much depends on the voltage).

    Note the famous equation P=IV. Current (C/s) times voltage (J/C) equals power, which can be measured in watts (J/s).

    Make sense?
     

    BenzylAcetate

    Just Peachy
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    Jun 17, 2011
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    1. Medical Student
      Yes i know all of this.

      But im wanting to know why amps kill you but volts dont.
      A cattle prod has high volts for pain, but low amps to reduce fatalities.

      Skin is very poorly conductive, so you need a high voltage for actual charge transfer. Heart tissue is maintained over a very small range of membrane potentials (-70-10mV) so large current would cause severe depolarization and subsequent cardiac arrest.
       
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      milski

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      1. Pre-Medical
        The voltage is not directly important - what matters is the current and for how long it flows. Certain minimal current needs to flow through your heart for a certain period to kill you - we are talking about milliamps of current and seconds of time. The ways to stay safe are either by limiting current or the time of discharge. I don't know what exactly the current from cattle prod is but I'm willing to bet that it is applied only for a very brief moment. In that case what makes it safe is more related to the duration of the electric shock.

        Also, it's very bad idea to think that volts will not kill you. With the same application points and with no limit of the charge, higher potential will be more dangerous (and will lead to higher current).
         

        howlovely

        Full Member
        May 9, 2012
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        1. Pre-Medical
          Voltage and amperage were described to me as a waterfall:

          Voltage is the electric potential that an object has, so think of it as the height of the waterfall. The bigger the voltage, the higher the water falls before it is grounded.

          Amperage, or current, is the amount of water that is moved over the waterfall per second.

          If something has a high voltage but low current, then it would be like a stream going over a cliff. Unless the cliff is extremely high, the stream won't be doing much damage when it hits the bottom.
           

          rjosh33

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          Jul 28, 2011
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          1. Medical Student
            Yes i know all of this.

            But im wanting to know why amps kill you but volts dont.
            A cattle prod has high volts for pain, but low amps to reduce fatalities.

            Sorry, didn't mean to sound like I was talking down to you.

            But, really, if you already understood what I said, then there shouldn't be a question of volts vs. amps killing you. The two are intertwined. Volts are the potential to deliver energy, while amps are the "vehicle" of delivering said energy. The following is straight from my physics textbook:

            "The seriousness of a shock depends on the applied voltage and on the effective resistance of the body. Living tissue has low resistance since the fluid of cells contains ions that can conduct quite well. However, the outer layer of skin, when dry, offers high resistance and is thus protective.

            Most people can "feel" a current of about 1 mA. Currents of a few mA cause pain but rarely cause much damage in a healthy person. Currents above 10 mA cause severe contraction of the muscles, and a person may not be able to release the source of the current. Death from paralysis of the respiratory system can occur. If a current above 80 to 100 mA passes across the torso, so that a portion passes through the heart for more than a second or two, the heart muscles will begin to contract irregularly and blood will not be pumped. This condition is called ventricular fibrillation."
             
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