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The voltage and an electric heater

  1. Dec 27, 2014 #1
    1. The problem statement, all variables and given/known data
    A 660[W] heater can work on 120[V]. if the voltage decreases to 110[V] what is the power that it consumes?

    2. Relevant equations
    $$V=iR$$
    $$P=iV$$
    For pure resistance: ##P=i^2R##

    3. The attempt at a solution
    The current at 660[W]: ##P=i\cdot 120\rightarrow i=5.5[A]##
    The resistance: ##660=5.5^2\cdot R\rightarrow R=22[\Omega]##
    The new current: ##V=iR\rightarrow 110=i\cdot 22\rightarrow i=5[A]##
    The new power consumption: ##P=i\cdot V=5\cdot 110=550[W]##
    And with another method: ##P=i^2\cdot R=5^2\cdot 22=550[W]##
    It is written that it should be 500[W]
     
  2. jcsd
  3. Dec 27, 2014 #2

    gneill

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    Staff: Mentor

    Your calculations look fine. The supposed answer is not correct.
     
  4. Dec 27, 2014 #3
    Thanks, gneil
     
  5. Dec 27, 2014 #4

    haruspex

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    Science Advisor
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    2016 Award

    My guess is the rated power should be given as 600W, not 660W.
     
  6. Dec 28, 2014 #5
    Thank you too, haruspex, but the other partial answers to this question, which i didn't fully copy here, fit 660[W], but i guess this problem is solved
     
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