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Homework Help: 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?

    http://www.vcaa.vic.edu.au/vce/studies/physics/pastexams/physics12004.pdf

    Question 5, page 11

    Thanks
     
  2. jcsd
  3. Jul 26, 2008 #2

    Mapes

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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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