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Homework Help: Power math question

  1. Oct 12, 2005 #1
    Suppose that a person has a resistance of 13.0 kiloohms as part of a circuit which passes through his hands. This person accidentally grasps the terminals of a power supply with a potential difference of 16.0 V.
    PART A:If the internal resistance of the power supply is 2100 ohms , what is the current through the person's body?
    I calculated the current to be 1.06×10−3 A by using the equation I = V/(R_p + R_i)
    PART B: To find the power dissipated in his body I thought you use the equation P = I*V so P =(1.06*10^-3 A)*(16.0V) which gave me 1.70*10^-2 which is wrong. What I am doing wrong??
    Thank you for your help
  2. jcsd
  3. Oct 12, 2005 #2


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    Homework Helper

    Firstly I'd just like to comment that the resitance through a person's hand is a bit higher than that. In the mega, if not giga ohm range.

    By using P = IV, you have essentiatlly calculated the power DELIVERED by the power suppy instead of the power being absorbed by the person. If you want to use P=IV, then the V must be the potential difference across the person which can be calculated using voltage division. The easier equation would be [tex] P = I^2R[/tex] where you use R of the hands.
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