# Power math question

1. Oct 12, 2005

### Tcat

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??
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 $$P = I^2R$$ where you use R of the hands.