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!

Current in parallel circuits

  1. Feb 19, 2007 #1
    This is just a general question... when trying to solve for the current in each resistor in a parallel circuit, how do you go about setting it up? (I know that the equation V=IR comes in handy...)
  2. jcsd
  3. Feb 19, 2007 #2


    User Avatar
    Gold Member

    You could use the current divider rule. That would require you to find the total current in the circuit. Whats wrong with using V=IR?
  4. Feb 19, 2007 #3
    What is the current divider rule?
  5. Feb 19, 2007 #4


    User Avatar
    Gold Member

    Its used to find current when resistances are hooked up in parallel with each other. Here is a wiki picture that should clear things up for you:
  6. Feb 19, 2007 #5
    That really helped! But if the circuit has three branches in parallel, does the formula change to I1=Itotal x ((R2+R3)/(R1+R2+R3)) ?
  7. Feb 19, 2007 #6


    User Avatar
    Gold Member

    It changes a little when we have more than two resistances. Lets consider a circuit with three parallel branches. We know that the voltage drop across any resistor in a parallel circuit is equal to that of the source:

    [tex] I_x = \frac{V_s}{R_x}[/tex]

    [tex]V_s = I_TR_T[/tex] <--the source voltage is equal to the total current times the total resistance.

    Now substituting [itex]I_TR_T[/itex] for Vs in the first equation (Ix).

    [tex]I_x = \frac{I_TR_T}{R_x}[/tex]

    We can therefore conclude that the current through any parallel resistor is in fact:
    [tex]I_x = \frac{R_T}{R_x}\cdot I_T[/tex]

    Hope it helps/
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Current in parallel circuits