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Homework Help: Electrical Resistance Exercise, please help.

  1. May 12, 2007 #1
    Please help with the following exercise:

    How much should the electrical resistance of a light bulb be in order to consume a power of 60W if a voltage of 220V is applied?

    This is how I solved it:

    Power= Voltage^2 / Resistance

    60W = 220V^2 / R

    R = 807 ohms

    Is it correct? Thank you.
  2. jcsd
  3. May 12, 2007 #2


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    Staff Emeritus
    Science Advisor

    Yes - the answer is correct.

    for DC, Power = Voltage * Current, or P = V*I, but I = V/R, so

    P = V2/R.

    In this application, V is the potential difference driving the current I through resistance R.

    When solving problems, it is best to write out the applicable equations so as to check one's understanding of the physics.
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