RLC Series Circuit Problem: Find V_source from V_R, V_L, V_C

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SUMMARY

The discussion focuses on calculating the source voltage (V_source) in an L-R-C series circuit using the given rms voltages across the resistor (V_R = 32.0 V), capacitor (V_C = 90.1 V), and inductor (V_L = 51.5 V). The correct formula to determine the source voltage is Vs = sqrt{ Vr^2 + (VL - Vc)^2 }. The user initially attempted to convert rms values to peak voltages, which is unnecessary since the source voltage can be calculated directly using rms values. The application of Kirchhoff's rules and phasor diagrams is emphasized for understanding the relationships between the voltages in AC circuits.

PREREQUISITES
  • Understanding of L-R-C series circuits
  • Knowledge of rms and peak voltage relationships
  • Familiarity with Kirchhoff's voltage law
  • Basic skills in phasor diagrams for AC analysis
NEXT STEPS
  • Study the application of Kirchhoff's laws in AC circuits
  • Learn how to construct and interpret phasor diagrams
  • Explore the concept of impedance in L-R-C circuits
  • Investigate the effects of frequency on circuit behavior
USEFUL FOR

Electrical engineering students, circuit designers, and anyone involved in analyzing or designing AC circuits will benefit from this discussion.

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Homework Statement


In an L-R-C series circuit, the rms voltage across the resistor is 32.0 , across the capacitor it is 90.1 and across the inductor it is 51.5 .
What is the rms voltage of the source?


Homework Equations



Well there are lots of equations V_rms =V/sqrt(2)
V_R=IR
V_L=IX_L(I[tex]\omega[/tex]L)
V_C=IX_c(I/([tex]\omega[/tex]C)

The Attempt at a Solution



So what i did was convert all the values from rms into their amplitude voltages and summed them. Then took the resultant rms of that answer. This is not correct however.

I was using kirchhoffs rules of the sum of voltages around loop =0. Does this principle hold true in this situation?
 
Last edited:
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For an AC circuit, the voltage across the source is equal to the vector sum of the voltages of the components. Using the phasor diagram, you can graphically determine the direction of the source voltage, if it leads the current or not, and how to find the vector sum of the voltages. Rms and peak amplitude voltage are proportional by sqrt{2}, so you don't need to convert to peak and then back to rms, just leave everything in rms and the source voltage will be in rms. The source voltage is related to the other voltages like this:

Vs = sqrt{ Vr^2 + (VL - Vc)^2 }
 
GRB 080319B said:
For an AC circuit, the voltage across the source is equal to the vector sum of the voltages of the components. Using the phasor diagram, you can graphically determine the direction of the source voltage, if it leads the current or not, and how to find the vector sum of the voltages. Rms and peak amplitude voltage are proportional by sqrt{2}, so you don't need to convert to peak and then back to rms, just leave everything in rms and the source voltage will be in rms. The source voltage is related to the other voltages like this:

Vs = sqrt{ Vr^2 + (VL - Vc)^2 }

Thank you so much! I've ben stuck on this for so long.
 

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