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Varying the voltage of a light bulb

  1. Jul 26, 2008 #1
    Hey guys, was wondering if you could help me with this question:

    What determines the brightness of a lightbulb?

    I think it would be power (and therefor voltage and current since P = VI) as power is used in the measurement of energy delivered. Why is it the case then that, from the questions i am doing, it states that if you have a simple circuit such as the one shown in the following link (page 11, question 5), why doesnt the brightness vary when one part of the parrallel circuit is removed?


    Question 5, page 11

  2. jcsd
  3. Jul 26, 2008 #2


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    I don't see the contradiction. There's no power associated with the removed bulb, so it's dark. The power is unchanged for the others*, so their brightness is unchanged.

    *P = VI = V2/R, and voltage and resistance are constant.
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