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!

Simple Power in a circuit problem

  1. Jan 24, 2007 #1
    1. The problem statement, all variables and given/known data

    Determine the missing quantity in the circuits in figure below.

    2. Relevant equations

    P = IV = V^2 / R
    V = IR

    3. The attempt at a solution

    From the diagram, I know the current is flowing opposite to the reference direction (because of the negative current). I used the equation, P = VI.

    So,

    -20 W = V (-2 A)... I get V is equal to 10 V. It says something is wrong, what am I doing wrong?

    I know since the power is negative, and due to Passive Sign Convention, it is supplying power. I'm kind of stuck as to why it doesn't work out the way I did it. Thanks.
     

    Attached Files:

  2. jcsd
  3. Jan 24, 2007 #2
    I'm sorry, I re-read the text in the mean while and I figured this out. I forgot to change the polarities and switch V_1 to -(V_1).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Simple Power in a circuit problem
  1. Simple Circuit Problem (Replies: 2)

Loading...