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Power PLEASE Help Test THURSDAY

  1. Feb 12, 2008 #1
    Power...PLEASE Help...Test THURSDAY!!!

    I am having a hard time understanding why some power equations for finding the power dissipated by light bulb(s) don't work. I have...
    P = IV = I^2R = V^2/R
    But for some of the problems these equations are getting me different numbers for each one! I am getting confused and I now don't know when to use which one and I have a test on Thursday! One example...

    Two 97 W (114 V) lightbulbs are wired in series, then the combination is connected to a 114 V supply. How much power is dissipated by each bulb?

    I found I using P/V = .851 then when I go to find the power the only equation that gets me the right answer is P = V^2/R then divide by 2 = 24.3 W
     
  2. jcsd
  3. Feb 13, 2008 #2

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    The current reduces through each when connected in series, so that the power is not just 2*97 W. You have to find the V across each or find I.
     
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