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: Calculate the Current, Lost Volt and P.d across parallel resistors?

  1. May 10, 2008 #1
    1. The problem statement, all variables and given/known data
    http://img508.imageshack.us/img508/9121/10052008ei3.png [Broken]
    (a) Calculate the Current across parallel resistors.
    (b) Calculate the lost volt across parallel resistors.
    (c) Calculate the potential difference across parallel resistors.

    2. Relevant equations
    [tex]I = \frac{V}{R}[/tex]

    [tex]Lost \ Volt = Ir[/tex]

    [tex]V = IR[/tex]

    3. The attempt at a solution
    (a) [tex]1.5A[/tex] (I just added the currents of the parallel resistors.)

    (b) [tex]Lost \ Volt = Ir[/tex]

    [tex]= 1.3 \times 1.5[/tex]

    [tex]= 1.95V[/tex]

    [tex]= 2.0V[/tex]

    (c) Need Help in solving it...

    Thnx in advance
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. May 10, 2008 #2


    User Avatar
    Homework Helper

    What exactly does "lost volt" refer to?

    For (c), recall what is the expression for voltage across a resistor. Also try to recall what so special about the potential difference across parallen circuit components. Then just plug in the numbers and you're done.
  4. May 10, 2008 #3
    That the problem, I don't really know what Lost Volt is?!

    (c) [tex]V_1 = IR = 1.17 \times 6 = 7V[/tex]

    [tex]V_2 = IR = 0.33 \times 21 = 7V[/tex]

    So, the voltage across the parallel resistors is [tex]7V[/tex] ?
  5. May 10, 2008 #4


    User Avatar
    Homework Helper

    Yes, that should be it. Anyway, I have no idea what "lost volt" refers to. Maybe you could ask your teacher who set the question.
  6. Nov 25, 2010 #5
    I'm pretty sure the lost volt is the resistance inside the battery. Once you work out the lost volt you can minus that from the voltage of the battery and work out the real value of V. Most questions dont include thw lost volt because it is quite small and considered negible. I think they are probably just making you aware of it and know hoe=w to calculate it.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook