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!

Finding current in a resistor circuit

  1. Oct 12, 2015 #1
    1. The problem statement, all variables and given/known data
    hwproblem.jpg

    There are several parts, but the part I'm stuck on is: what happens if a jumper is placed from node A to node B? Calculate V_A and V_B, and magnitude and direction of the current through the jumper. The resistor values are R1=R2=2 kohms, R3=R4=1 kohm.

    2. Relevant equations

    Kirchhoff's voltage and current laws.

    3. The attempt at a solution

    Okay, so I know that connecting a wire between A and B will make V_A=V_B. I was wondering if there's an intuitive way to find the current quickly without using Kirchhoff's loop rules. I tried Kirchhoff's voltage law and it seems that the current is zero. But I'm not sure if I'm right.
     
  2. jcsd
  3. Oct 12, 2015 #2

    berkeman

    User Avatar

    Staff: Mentor

    Correct. Once you short the middle part, you can combine the upper resistors into their parallel combination value, and the same with the lower ones.

    If you used a resistor instead of a shorting wire to connect A to B, the answer might be different. :smile:
     
    Last edited: Oct 12, 2015
  4. Oct 12, 2015 #3

    gneill

    User Avatar

    Staff: Mentor

    You could take advantage of the symmetry of the situation. Pencil in the given resistor values on the diagram. Can you "see" what the values of V_A and V_B will be (before connecting the jumper betwixt them)? Does that suggest anything about what the jumper current might be once it's connected?
     
  5. Oct 12, 2015 #4
    So before connecting the jumpers, V_A and V_B are already equal, using the voltage divider equation right? They're both 2.5 V. If they weren't equal before, would there be a current through the jumper?
     
  6. Oct 12, 2015 #5

    gneill

    User Avatar

    Staff: Mentor

    Right.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted