How about?
P (Watts) = V * I * PF always true
PF =1 for a resistive load
For AC loads where the current waveform is sinusoidal AND the current waveform is sinusoidal then P = Vrms*Irms*Cos(theta)
Cos(theta) is the phase angle between voltage and current
When the voltage waveform is sinusoidal and hence periodic and the current waveform is non-sinusoidal, but periodic (typical), you cannot measure the phase angle directly to determine the PF.
P (Watts) = V * I * PF always true
PF =1 for a resistive load
For AC loads where the current waveform is sinusoidal AND the current waveform is sinusoidal then P = Vrms*Irms*Cos(theta)
Cos(theta) is the phase angle between voltage and current
When the voltage waveform is sinusoidal and hence periodic and the current waveform is non-sinusoidal, but periodic (typical), you cannot measure the phase angle directly to determine the PF.
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