# Reactive and Active Power

When I am calculating the power in the circuit , do I use the RMS values , or the peak values and why ?

NascentOxygen
Staff Emeritus
RMS values are standard.

Thank you !

sophiecentaur
Gold Member
When I am calculating the power in the circuit , do I use the RMS values , or the peak values and why ?
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.

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.
Sorry , it would be sinusoidal in nature. What did you mean by enough for jazz though ?

sophiecentaur
Gold Member
Sorry , it would be sinusoidal in nature. What did you mean by enough for jazz though ?
"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" • Nile Anderson
"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" Cool thank you so much for your input , it was really helpful