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!

Potential difference between two points on a circuit

  1. Apr 19, 2016 #1
    1. The problem statement, all variables and given/known data

    n76vt.png

    The circuit is shown as above.
    If ε = 3 volt and each resistor has 2 ohm resistance, then what's the potential difference between point B and point D ?

    A. 4
    B. 3
    C. 2
    D. 1
    E. 0

    2. Relevant equations

    V = I R
    R series = R1 + R2 + ..
    1/ R parallel = 1/R1 + 1/R2 + ...

    3. The attempt at a solution

    The circuit is very weird. I don't even know how to start.
     
  2. jcsd
  3. Apr 19, 2016 #2

    cnh1995

    User Avatar
    Homework Helper

    Are you familiar with Kirchhoff's laws?
     
  4. Apr 19, 2016 #3
    Yes, of course.. KVL and KCL..
    Okay, I'll use KVL for the two triangles

    Triangle ADC

    4IR = ε
    I = ε/4R = 3/8 ampere

    The current in triangle ABC also 3/8 ampere, right ? (The resistance are equal also the emf)

    But, what's the potential difference between point B and D?
     
  5. Apr 19, 2016 #4

    cnh1995

    User Avatar
    Homework Helper

    Assume current through diagonal AC as i and current through ABC as i1. So, current through ADC is i-i1. Using these currents, write KVL and you'll get values for i and i1.
    Actually, this problem can be solved by observation only, using the symmetry of the circuit.
     
  6. Apr 19, 2016 #5
    ##Triangle\ ABC \\
    2I_1R+2IR - \varepsilon = 0 \\
    4I_1 + 4I = 3\\
    Triangle\ ADC \\
    2((I-I_1)R) + 2IR - \varepsilon = 0 \\
    4IR-2I_1R = 3 \\
    8I - 4I_1 = 3 \\##

    Solving the equation, I get i = 0.5 A, and i1 = 0.25 A, and it means that i2 = 0.25 A
    How to determine the potential difference between B and D ??

    Yeah, I also see that it's kinda like the Wheatstone bridge, isn't it ??
    But, eventually, the current through diagonal AC is not zero (not as I thought it would be in Wheatstone bridge)..
    Please help me
     
  7. Apr 19, 2016 #6

    cnh1995

    User Avatar
    Homework Helper

    Good!
    Let's say point A is at a potential Va and point B is at potential Vb. Voltage drop across the resistor between A and B is Va-Vb. What is the value of this voltage drop? You know the currents now.
     
    Last edited: Apr 19, 2016
  8. Apr 19, 2016 #7
    Vb = 3 - 0.5 * 2 - 0.25 * 2 = 1.5 V
    Vd = 3 - 0.5 * 2 - 0.25 *2 = 1.5 V
    The potential difference is zero, right ?

    Anyway, is this circuit a Wheatstone bridge?
     
  9. Apr 19, 2016 #8

    cnh1995

    User Avatar
    Homework Helper

    Right.
    Yes. Supply is connected between A and C and output is taken between B and D.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted