1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    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.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Power math question
  1. Solar power maths (Replies: 3)

  2. Question on Power (Replies: 1)

  3. Power question (Replies: 7)