Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Find power in resistors

  1. Feb 23, 2012 #1
    1. The problem statement, all variables and given/known data

    Three resistors, R1 = 32 Ω, R2 = 45 Ω, and R3 = 60 Ω, are connected in a multiloop circuit, as shown in the figure. Determine the amount of power dissipated in the three resistors.

    2. Relevant equations

    loop law
    junction law

    3. The attempt at a solution

    (1) i1 +i2 +i3 = 0

    (2) 9 - 45 i2 + 32 i1 = 0

    (3) 15 +60 i3 + 9 - 45 i2 = 0

    when you use the loop law, don't you have to go the same direction with every loop?
    In the equation (3) it is going clockwise, and in equation (2) it is going counter-clockwise.
    Is this wrong?
  2. jcsd
  3. Feb 23, 2012 #2


    User Avatar

    Staff: Mentor

    You don't have to go the same direction with every loop. All you have to do is respect the potential drops/rises as specified by the chosen current directions (as indicated by the arrows) as you traverse the components during your "tour" around the loop.
  4. Feb 23, 2012 #3


    User Avatar
    Science Advisor
    Homework Helper

    Hi Cisneros778! :smile:
    No, it doesn't matter which way round you go …

    if you went the other way round one loop, everything would be multiplied by -1, wouldn't it? :wink:

    btw, it might be easier to take the outside loop rather than the bottom loop (the outside loop is the sum of the other two), since it has one less term in it (and one less chance of making a mistake! :biggrin:)​
  5. Feb 23, 2012 #4
    Thank you so much. I got the answers correct!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook