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Salt water and tap water conducting electricity - help appreciated

  1. Mar 10, 2012 #1
    Salt water and tap water conducting electricity - help appreciated :)

    Hello,

    Thanks in advance for helping me with my question! I'm so excited to find this physics forum of such talented people.
    My question is, I know that salt water conducts electricity more than tap water due to the ions dissolved. Does that mean that a person touching a live wire/prong with a finger wet in salt water will feel LESS of a shock than a person touching a live wire/prong with a finger wet in tap water?

    In other words, will the electrical charge instead be dispersed among the salt water compared to the tap water, and some of the electrical impact lost there?

    Will the electric shock be substantially different, or will the person in both scenerios feel the same type of shock ( not noticeable difference).

    Thanks in advance for your help :)
     
  2. jcsd
  3. Mar 11, 2012 #2
    Re: Salt water and tap water conducting electricity - help appreciated :)

    Help, anyone please? :(

    Thanks so much in advance!
     
  4. Mar 11, 2012 #3

    marcusl

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    Re: Salt water and tap water conducting electricity - help appreciated :)

    Welcome to PF! We will try to help answer your question.

    You have some misconceptions about electricity, conduction, and electric shock. To receive a shock, electric current must flow through the body. A tragic scenario is touching a live wire, as you say, while standing on a wet floor--current flows from the wire (through a finger, say), through the body and out the feet into the ground. Worse yet is if you are sitting in metal bathtub, since the tub is well-grounded through the cold water faucet, and since the large surface area of wet body provides a particularly low resistance return path to ground. Since current can flow through the heart and disrupt its rhythm, death can result. The water acts to reduce the normally high resistance of your skin, increasing the current flow and the severity of shock. Salt water is an even better conductor, so is somewhat more hazardous.

    I hope that helps explain the science behind shocks.
     
  5. Mar 11, 2012 #4
    Re: Salt water and tap water conducting electricity - help appreciated :)

    Hi Marcusl,

    thanks SO MUCH for replying. You're awesome! Just to clarify - so you're saying you'll get less of a shock if you touch a live wire with wet fingers, compared to someone who is touching a live wire with dry fingers but standing on wet ground? how do the electrons know that the person is standing on wet ground?

    Thanks so much :) have a great day!!
     
  6. Mar 11, 2012 #5

    marcusl

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    Re: Salt water and tap water conducting electricity - help appreciated :)

    No, I didn't say that at all. Dry unbroken skin normally has a high resistance to the flow of electric current, although you can still get shocked, of course. Any parts that are wet have low resistance, vastly increasing the danger.
     
  7. Mar 13, 2012 #6
    Re: Salt water and tap water conducting electricity - help appreciated :)

    To get a better understanding, you need to know some basic electrical engineering, so here's a basic example:

    If you connect a battery in some way, an electrical current I will flow from (+) to (-) (electrons will actually go from (-) to (+), but that's another story, the current direction is a convention).

    The current I depends on Ohm's law, I=V/R, where V is the voltage (electrical potential difference) and R the total resistance of what the battery is connected to. Let's say the connection is (+)-wire-lamp-wire-(-), then the total resistance R is the sum of the wire resistance and the lamp resistance.

    The electrons don't know what to do; they are attracted to (+) and they start to flow if there is a connection between (+) and (-) in the first place, and the current depends on the resistance R of the whole connection between (+) and (-) as I described above.

    So in the case with the body, the live wire (+) and e.g. the ground (-) is (together) the battery, and the connection is the body. The resistance of the body depends on a number of different things; e.g. skin resistance, skin area that is exposed to (+) and (-), water that decreases resistance etc, as marcusl mentioned above. The lower the resistance R is, the larger the current I gets, that's Ohm's law. And larger current = more dangerous.

    Note: One should always be VERY careful when dealing with electrical things, even disconnected things can be dangerous, e.g. capacitors. A couple of safety measures to keep in mind when dealing with electrical circuits are:

    1) Don't do anything unless you really know what you are doing.
    2) Respect electricity! It can easily get lethal! Make sure the power is off, cords removed etc.
    3) Always use electrically insulated tools
    4) Always make sure hands, environment etc. is dry
    5) Remove any metal from body (e.g. rings etc)
    6) When dealing with potentially dangerous things; keep one hand in the pocket ("insulated"). Then there is a much lower risk that a current can flow from one hand through the body to the other hand. But a person should not do any such things ever if the person is not a professional.

    More info:
     
    Last edited: Mar 13, 2012
  8. Mar 13, 2012 #7
    Re: Salt water and tap water conducting electricity - help appreciated :)

    Think of salty water does NOT resist the flow of current, while tap water resist the flow of current. So when you touch a live wire via salty water you get a full shock because this salty water does not resist the current flowing toward your body. However if you have tap water (more resistive) then it would resist the flow of current and you get less of a shock.

    I suggest you don't try any of them by the way, both would be painful experiments!
     
  9. Mar 13, 2012 #8

    jim hardy

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    Re: Salt water and tap water conducting electricity - help appreciated :)

    Get a cheap multimeter from Walmart, the kind with a needle. I like the yellow GE in hardware department it's just $9.95..

    Set it to highest ohms scale.
    Now the needle will indicate ease of passing current between test leads:
    no deflection = impossible
    full deflection = easy

    short the leads together to confirm. While they're shorted adjust the knob on side for zero ohms indication, which is full deflection. (ohms scale is top one that's non-linear, usually black )

    Now grab the leads tightly between two fingers and observe small deflection, write down reading
    repeat with fingers wetted with tap water
    and with fingers wetted with salted tap water

    and observe readings.
    That should show you that current can get into your body where the nerves are if you degrade skin's insulating properties with water be it fresh or salty.


    DO NOT TRY THIS WITH ANY OTHER APPARATUS THAN A TEST METER.
    Stay away from electric outlets.

    I know firsthand you cannot hold onto a 12 volt car battery when you're out in a boat and covered with ocean spray.
     
    Last edited: Mar 13, 2012
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