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Calculate percentage change in heat output

  1. May 11, 2012 #1
    1. The problem statement, all variables and given/known data
    A 500W heating unit is designed to operate on a 115V line. If the line voltage drops to 110V, calculate the percentage drop in heat output.


    2. Relevant equations
    R=V^2/P


    3. The attempt at a solution
    P=V^2/R

    Use V=115, then use V=110, use Power P=500...but not sure how

    p.s. I am a UK Physics student. I was wondering could you also say whether you are in the UK or US or....
     
    Last edited: May 11, 2012
  2. jcsd
  3. May 11, 2012 #2
    Find the resistance of the heater. Use that value of resistance and 110 volts to find new power output. %=(initial-finial)*100/initial
     
  4. May 11, 2012 #3
    Thanks thats great! I've done it now
     
  5. May 11, 2012 #4
    I got an answer of 8.5%! sounds right....

    Btw what do people think about the questions on online-exam-solutions?
     
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