• Support PF! Buy your school textbooks, materials and every day products via PF Here!

RLC circuit problem

  • Thread starter Saitama
  • Start date
1. The problem statement, all variables and given/known data
A series LCR circuit with ##L=0.125/\pi## H, ##C=500/\pi## nF and ##R=23\,\Omega## is connected to a 230 V variable frequency supply. For what reactance of circuit, the power transferred to the circuit is half the power at resonance?

2. Relevant equations

3. The attempt at a solution
At resonance,
Hence, the power transferred at resonance is given by ##P=V^2_{rms}/R=2300\,\,W##.

When the power transferred is half, let the reactance be Z, hence,
As per the question:
$$\frac{V^2_{rms}}{Z}\frac{R}{Z}=\frac{1}{2}\times 2300$$
$$\Rightarrow \frac{230\times 230 \times 23}{Z^2}=\frac{1}{2}\times 2300$$
$$\Rightarrow Z=23\sqrt{2} \,\,\Omega$$
But this is incorrect. The correct answer is ##23\,\,\Omega##. :confused:

Any help is appreciated. Thanks!


Homework Helper
Gold Member
The way you've defined it, Z is the impedance, not the reactance.

The reactance, X is such that Z = R + jX, and it's the X that you need to solve for.

Note that the magnitude squared of Z is, Z2 = R2 + X2. That will come in useful. :smile:
Last edited:
The way you've defined it, Z is the impedance, not the reactance.
Ah yes, thanks a lot collinsmark! :smile:

Want to reply to this thread?

"RLC circuit problem" You must log in or register to reply here.

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving