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Physics help, !

  1. Feb 27, 2008 #1
    Physics help, urgent!

    1. The problem statement, all variables and given/known data

    The damage caused by electric shock depends
    on the current fowing through the body;
    1 mA can be felt and 5 mA is painful. Above
    15 mA, a person loses muscle control, and 70
    mA can be fatal. A person with dry skin has a
    resistance from one arm to the other of about
    70000 ohms *. When skin is wet, the resistance
    drops to about 5000 ohms .
    a.)What is the minimum voltage placed across
    the arms that would produce a current that
    could be felt by a person with dry skin? An-
    swer in units of V.
    b.) Using the same electric potential as in Part 1,
    what would be the current if the person had
    wet skin? Answer in units of mA.

    2. Relevant equations


    3. The attempt at a solution

    I got part a right. It's 70 V.
    For b.) I did 5000/70. but it wasn't right. Can someone help?
  2. jcsd
  3. Feb 27, 2008 #2

    Doc Al

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    Staff: Mentor

    upside down?

    Compare what you did to the formula.
  4. Feb 27, 2008 #3


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    Homework Helper

    answer why you tried 5000 / 70 ?

    what does "Part 1" refer to?
  5. Feb 27, 2008 #4

    I should have done 70/5000 because V=70 and R=5000.
    I got .014 but it is still wrong.

    Part 1 means part a.
  6. Feb 27, 2008 #5

    Doc Al

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    Staff: Mentor

    Make sure you follow directions and give the answer in the correct units.
  7. Feb 27, 2008 #6

    I got .014 mA. Can someone explain what I'm doing wrong?
  8. Feb 27, 2008 #7

    Doc Al

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    Staff: Mentor

    Check your units. Volts/Ohms = Amps.
  9. Feb 27, 2008 #8
    I know this has nothing to do with the question, but the question is quite simply dangerously wrong. Wet or broken skin is closer to 1000 Ohms and a wound can be lower. No one should handle electricity based on the information in the question. Source: NIOSH
  10. Mar 6, 2010 #9
    Re: Physics help, urgent!

    hey can u play explain to me how u got part a?
  11. Mar 6, 2010 #10

    Doc Al

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    Staff: Mentor

    Re: Physics help, urgent!

    Use Ohm's law, the formula given in post #1.
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