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!

Electricity: voltage calculation in serial

  1. Apr 14, 2017 #1
    1. The problem statement, all variables and given/known data
    Calculate the voltage U.
    The voltmeter gives a value of 80V.
    exercise.png

    3. The attempt at a solution

    3RI + 4RI - U = -80
    How can I create a System of Linear equations if I have only one equation?
    Do I miss something?

    My answer sheet says U = 150V.
     
  2. jcsd
  3. Apr 14, 2017 #2
    What is 'R'? Is it a variable, or does it represent "resistor"? I guess it really doesn't matter. If it is a variable, the R's should cancel out. You know that the voltage across the 2 inside resistors is 80 V, so you should be able to come up with a second equation for that.
     
  4. Apr 14, 2017 #3
    Let I be the current through the circuit. The V to the drop at 2R and 6R, so
    2RI + 6RI = 80
    8RI = 80
    RI = 10

    For the whole circuit,
    U - 3RI - 2RI - 6RI - 4RI = 0

    Try to take it from there!
     
  5. Apr 14, 2017 #4
    Thanks, I got it.
     
  6. Apr 14, 2017 #5
    RI = 10
    U - 3RI - 2RI - 6RI - 4RI = 0
    U - 3*10 - 2*10 - 6*10 - 4*10 = 0
    U - 30 - 20 - 60 - 40 = 0
    U - 150 =0
    U = 150V

    I found it, thanks for your help.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted