1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Circuits and Loop Rule

  1. Apr 10, 2010 #1
    1. The problem statement, all variables and given/known data

    Write the loop rule for each of the following circuits:

    2. Relevant equations
    Depending on the loop:
    -emf + IR1 + IR2 + .... + IRn = 0
    V = IR
    If in series: R1 + R2 + ... Rn = R
    If in parallel: 1/R1 + 1/R2 + ... 1/Rn = 1/R

    3. The attempt at a solution

    I really don't know how to do these because we usually only had 1 battery. But here's my shot:

    (A) Could you say that both batteries are in series and treat them as one battery, then say the R2 and R3 are in parallel?

    (B) and (C) I don't have the slightest clue. For (B), I don't know if you can say that R1, R2, and R3 are in series with emf3 there, and (C) we've never had a battery in parallel (We either had 1 battery or 2 batteries in series).
  2. jcsd
  3. Apr 10, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi DeadFishFactory! :wink:

    "Loop rule" means that you only consider one loop at a time … that means everything is in one (series) circuit.

    Forget the series and parallel rules … only apply Kirchhoff's rules …

    voltage gain across each battery is the voltage (obviously! :rolleyes:), and voltage drop across each resistor is I times R, and for each loop t all has to add to zero …

    what do you get? :smile:

    (and don't forget to draw the currents in … I1 I2 I3 etc)
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook