1. PF Insights is off to a great start! Fresh and interesting articles on all things science and math. Here: PF Insights

A battery-battery-resistor circuit

  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. Doc Al

    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. Oh, I got it now, Thanks!
Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook

Have something to add?