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Homework Help: Resistance of a light bulb question

  1. Oct 7, 2005 #1
    Hey guys I am having some trouble with this simple questions:
    What is the resistance of a light bulb that uses an average power of 75.0 W when connected to a 60.0 Hz power source having a maximum voltage of 190 V?


    (b) What is the resistance of a 120 W bulb?

    I tried doing it by (75/190)^2 * (2pi60) but this is not correct.
     
  2. jcsd
  3. Oct 7, 2005 #2

    Astronuc

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    One has to apply the equivalent of P = V I = V2/R = I2R for AC, so R = V2/P.

    Since it is pure resistance, i.e. no reactance, the voltage and current are in phase.

    Think of average and maximum.
     
  4. Oct 7, 2005 #3
    Ok, do i still have to multiply the 60hz by 2pi? Also, how do i handle it being connected to the power source?
     
  5. Oct 7, 2005 #4

    Astronuc

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  6. Oct 7, 2005 #5
    no but thanks for the link. I think that should of helped me get an idea
     
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