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Homework Help: Power and Batteries

  1. Feb 23, 2008 #1
    1. The problem statement, all variables and given/known dataAn Ordinary flashlight uses two D-cell 1.5V batteries connected in series. The bulb draws 450mA when turned on. A)Calculate the resistance of the bulb and the power dissipated. B) By what factor would the power increase if 4 D-cell batteries in series were used with the same bulb? (neglect heating effects)

    2. Relevant equations
    P=IV=I^2R=V^2/R V=IR

    3. The attempt at a solution
    I understand part A, and I got 1.4W for the power. For part B though, I keep getting that it's 2 times greater by doing P=IV where (.45A)(4 x 1.5) =2.7. but I know the answer is supposed to be 4 times. I'm pretty sure the current stays constant and that you add voltages, so I'm confused why it would be 4 and not 2.
  2. jcsd
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