Calculating Average Power LCR series circuit

AI Thread Summary
The discussion focuses on calculating the Q-factor and average power in a series LCR circuit. Participants clarify that the RMS voltage in the power formula refers to the voltage across the resistor. The impedance (Z) is determined by the combined resistance and reactance of the circuit components. It is confirmed that the average power can be calculated using the formula Pavg = Vrms²/R, emphasizing that the average power across the inductor and capacitor is zero. The conversation highlights the importance of understanding voltage measurements in relation to circuit components for accurate power calculations.
steejk
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Hi,

Im trying to calculate the Q-factor of a series LCR circuit.

I am struggling at how to calculate the average power. I want to find it using this formula:

pser.gif


What is the RMS voltage in the formula for - is it across the resistor, or what?

Any help is appreciated thanks.
 
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welcome to pf!

hi steejk! welcome to pf! :smile:
steejk said:
What is the RMS voltage in the formula for - is it across the resistor, or what?

from the two denominators, Z2 = R2 + (XL - XC)2 …

so Z must be the impedance across all three components (R L and C), and so V = IZ is the voltage (potential difference) across all three :wink:

(and V = IZ, so V2 = I2Z2, so Vrms2 = Irms2Z2)
 


tiny-tim said:
hi steejk! welcome to pf! :smile:


from the two denominators, Z2 = R2 + (XL - XC)2 …

so Z must be the impedance across all three components (R L and C), and so V = IZ is the voltage (potential difference) across all three :wink:

(and V = IZ, so V2 = I2Z2, so Vrms2 = Irms2Z2)

Thanks :)
 


tiny-tim said:
hi steejk! welcome to pf! :smile:


from the two denominators, Z2 = R2 + (XL - XC)2 …

so Z must be the impedance across all three components (R L and C), and so V = IZ is the voltage (potential difference) across all three :wink:

(and V = IZ, so V2 = I2Z2, so Vrms2 = Irms2Z2)

Can it also be said that Pavg = Vrms(across resistor)/R ?
 
steejk said:
Can it also be said that Pavg = Vrms(across resistor)/R ?

You mean Vrms(across resistor)2/R ?

Yes, the average power across L and C is zero, and the average power across R is VrmsIrms(across resistor) = Vrms(across resistor)2/R :smile:
 

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