Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Physics - Electricity

  1. Jan 29, 2007 #1
    1. The problem statement, all variables and given/known data
    The p.d. across a battery's terminals is 8.0V when connected to a 4ohm resistor. When this resistor is replaced with a 2ohm resistor the p.d. across it's terminals is 6.0V. What is the emf and internal resistance of the resistor?

    2. Relevant equations

    3. The attempt at a solution
    Code (Text):

    V = IR                              V = IR
    I  = V/R                            I  = V/R
       = 8/4                               = 6/2
       = 2A                                = 3A
    And then I just don't know what to do next. Help would be very appreciated. :)
  2. jcsd
  3. Jan 29, 2007 #2


    User Avatar

    Staff: Mentor

    I think the problem must ask "What is the emf and internal resistance of the battery"?


    You solve this kind of problem using the fact that you have two unknowns (Vbat and Rbat) and you have two equations (write the V=IR equation for the two situations that have been given to you).

    Does that help?
  4. Feb 1, 2007 #3
    Sorry for my very late reply, and yes it was supposed to be battery.

    You did help a lot. And just in case anybody else is struggling with a problem like this then I'll explain how I did it. I worked out that I could solve the equations simultaneously to find find the internal resistance of the battery and then you just need to do a simple V=IR calculation to find the emf of the Battery. ;)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook