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Average of square current

  1. Mar 27, 2009 #1
    1. The problem statement, all variables and given/known data

    A television set draws an rms current of 2.25 A from a 60 Hz power line.
    What is the average of the square of the current?


    2. Relevant equations

    Irms=square root of average of isquared

    3. The attempt at a solution

    i found the average of the current to be 0. I just keep getting 2.53, which is the wrong answer!
     
  2. jcsd
  3. Mar 27, 2009 #2
    You're not being asked to find the square of the average which is zero, you're supposed to find the average of the square.
     
  4. Mar 27, 2009 #3
    Hint: What's another word for average?
     
  5. Mar 27, 2009 #4
    do you do 2.25squared?
     
  6. Mar 27, 2009 #5
    Think about rms (root mean squared) and how the rms value is calculated. Compare that to the question.
     
  7. Mar 27, 2009 #6
    rms=1/squarerootof2*amplitude? i get 2.24
     
  8. Mar 28, 2009 #7
    Root Mean Square means we're taking the square root of the mean of the square. For a standard sine wave with maxima and minima at +1 and -1 and a mean of 0, when it is squared the maxima and minima become +1 and 0 and the mean is 0.5. The square root of the mean is 0.707.

    You are given the square root of the mean (average) of the square. If you square that value, what do you have?
     
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