1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Circuit Problem with Resistors connected in parallel and series

  1. Sep 23, 2012 #1
    1. The problem statement, all variables and given/known data
    A circuit is constructed with five resistors and a battery as shown. The battery voltage is V = 12.0 V. The values for the resistors are: R1 = 76.0 Ω, R2 = 149.0 Ω, R3 = 169.0 Ω, and R4 = 121.0 Ω. The value for RX is unknown, but it is known that I4, the current that flows through resistor R4, is zero.

    Find I1

    2. Relevant equations
    Resistors in Series
    Req = R1 + R2
    Veq = V1 + V2
    Ieq = I1 = I2

    Resistors in Parallel
    Req = (1/R1 + 1/R2)^-1
    Veq = V1 = V2
    Ieq = I1 + I2

    V = IR

    3. The attempt at a solution

    I know this has been asked elsewhere, but I read the other threads and couldn't get anything that helped me from them. I think I'm just having trouble visualizing the problem, and breaking the circuits into parts. I guess I'm having a lot of trouble visualizing how the energy travels through the circuit.

    I just can't picture it at all. I started by combining the circuits into R13, R4, and R2x. I'm guessing that for I4 to be zero, I14 has to equal I2. Ahh... If I can see this problem built once, I'm sure I could do it over and over again. Help plz...

    Attached Files:

  2. jcsd
  3. Sep 23, 2012 #2


    User Avatar

    Staff: Mentor

    How did you combine things? There are no series or parallel component opportunities in the circuit as drawn.

    Hint: If I4 is zero, what does that tell you about the potential across R4, and thus the potentials of the nodes that R4 connects to?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook