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Homework Help: Higher resistance of hair dryer

  1. Apr 6, 2007 #1
    A hair dryer has two settings: 840 W and 1320 W.
    (a) At which setting do you expect the resistance to be higher?
    840 W correct
    After making a guess, determine the resistance at each setting.
    (b) 840 W setting

    (c) 1320 W setting

    2. Relevant equations
    I am not exactly sure what equation to use to determine the resistance of the two settings.

    3. The attempt at a solution

    i tried numerous equations such as R =pla but i cant figure it out
  2. jcsd
  3. Apr 6, 2007 #2


    User Avatar

    Staff: Mentor

    I don't understand the "guess" part of the question, but whatever.

    Use the equation for power as a function of voltage and resistance. If you are in the US, then wall power for a hair dryer would typically be 110Vrms.
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