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!

A battery-battery-resistor circuit

  1. Aug 31, 2007 #1
    1. The problem statement, all variables and given/known data
    A circuit:
    Battery (1.5v) -- Battery (1.5v) -- Lamp(18 Ohm) and back to the first battery.

    The circuit is producing 0.25 Watt to the lamp. what is the inside-resistance of the batteries?

    2. Relevant equations

    3. The attempt at a solution
    we already have 18 Ohms from the lamp so the remining 36-18=18 is the answer.
  2. jcsd
  3. Aug 31, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You cannot assume that the voltage across the lamp is 3V--not when the batteries have internal resistance. Instead, find an expression for power consumption in the lamp in terms of I and R, and solve for the current.
    Last edited: Aug 31, 2007
  4. Aug 31, 2007 #3
    Oh, I got it now, Thanks!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: A battery-battery-resistor circuit