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!

Grounded circuit, 2 batteries and 2 resistors

  1. Mar 31, 2016 #1
    1. The problem statement, all variables and given/known data
    Picture a circuit grounded at the left lower corner. Then as you go up the left side of the circuit, you have a 9V battery. The top left corner is labeled a. Then on the top of the circuit, you have a 2 ohms resistor. Then on the right side of the circuit, you have a 6V battery. The right lower corner is labeled b. Then on the bottom side of the circuit you have a 1 ohm resistor.
    What is the value of the potential at points a and b?

    2. Relevant equations
    Kirchhoff's loop law
    I = Epsilon/R
    Delta Vr = - I*R


    3. The attempt at a solution

    First Kirchhoff's loop law to find the current in the circuit. I assumed the clockwise current was the same in both resistors.

    --> 9V - 2 I - 6V - 1 I = 0
    3V = 3I --> I = 1A

    I know the potential at point a is 9V. The potential at the lower left corner, where the circuit is grounded, is zero. As you go up the circuit, you have gained 9 V by "passing through" the 9V battery.

    Then you pass through the top resistor.
    The potential difference across that resistor is given by delta Vr = - I * R = -1A*2omhs =-2V. So by the time you reach the right top corner, you are at 9V-2V= 7V.

    Then you pass through the 6V battery. You go from the positive terminal to the negative terminal, so you lose 6V. Hence, at point b you are 7V-6V= 1V.

    Is my reasoning any good?
     
  2. jcsd
  3. Mar 31, 2016 #2

    cnh1995

    User Avatar
    Homework Helper

    What about polaritiy of the batteries? A diagram would be helpful.
     
  4. Mar 31, 2016 #3
    tmp_5375-20160331_170516-639066610.jpg
     
  5. Mar 31, 2016 #4

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Yes, that all works.
     
  6. Mar 31, 2016 #5
    Muchas gracias! !
     
  7. Apr 1, 2016 #6

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    You can also get to b by going "up" through the 1 Ohm....

    0 + (1*1) = 1V
     
  8. Apr 1, 2016 #7
    True that.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted