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Homework Help: Why doesn't a resistor burn up when its power rating is exceeded?

  1. Mar 12, 2010 #1
    1. The problem statement, all variables and given/known data

    The heating resistor is rated at 10ohms and 1W. By how much was its power exceeded? Why didn't the resistor burn up?

    This is a question taken from an Electrical Equivalent of Heat lab assignment... here is a link to the exact same lab we did...

    http://www.kbcc.cuny.edu/academicDepartments/PHYSCI/physics_12_14/pdf/Experiment4_EEquivalent_Heat.pdf [Broken]

    2. Relevant equations

    P=V^2/R where V=10ohms and R=10ohms

    3. The attempt at a solution

    P=10W but the resistors rating was 1W and I don't really know why it didn't burn up. My only guess is that some of the power was lost due to the water absorbing some of the energy given off by the resistor???

    Help! :confused:
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Mar 12, 2010 #2
    Your guess is correct. The ratings of power resistors do not take into account cooling them with water.
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