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Reactive and Active Power

  1. May 16, 2016 #1
    When I am calculating the power in the circuit , do I use the RMS values , or the peak values and why ?
  2. jcsd
  3. May 16, 2016 #2


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    RMS values are standard.
  4. May 16, 2016 #3
    Thank you !
  5. May 16, 2016 #4


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    I may be being difficult but what circuit and where is the value of the power, relevant? The peak power in a circuit with significant reactive elements in it could be very relevant - particularly if the waveform is not close to a sinusoid. RMS is certainly near enough for Jazz in most cases.
  6. May 16, 2016 #5
    Sorry , it would be sinusoidal in nature. What did you mean by enough for jazz though ?
  7. May 17, 2016 #6


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    "Near enough for Jazz" is a common expression which means 'accurate enough for the purpose'. When you read an unfamiliar idiom, Google is almost certain to help you with it. There a dozens of hits for "near enough for jazz".
    Measuring Power in an electrical circuit has a few issues. If you really want to know the power being dissipated in a component (Resistor,light bulb, LED, motor - you name it) you need to know both the instantaneous Volts and the Current. Then the Mean power for any component is the average value of VI, over a given time. That involves no assumptions and involves measurements of two quantities. If the component is pure Ohmic resistance then you can use
    Instantaneous Power = V2/R or I2R and use either just V or I.
    To find the average power - say over a cycle or an hour, you average all those instantaneous values of power. The 1/√2 figure that people use for working out RMS power from Peak Volts (for instance) definitely assumes a sine wave and a pure resistance and would not work perfectly for any other waveforms or non ohmic loads.
    So "you pays your money and you takes your pick" :wink:
  8. May 18, 2016 #7
    Cool thank you so much for your input , it was really helpful
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