Clarification on Physics problem

  • Thread starter cseet
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In summary: So, to find I_{rms} at any given \omega, we would use:I_{rms} = V_{rms} * \omega^2 = \frac{V_{max}}{\sqrt{2}} * \omega^2
  • #1
cseet
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Hi all,

I've got this physics problem, I've tried solving it but do not know for sure the steps I took are correct. pls kindly advise and redirect me if I've got it wrong... thanks

A series RLC circuit with L=11mH, C=2.9uF, and R=4.3ohm is driven by a generator with a max emf of 155V and a variable frequency w (omega)

a) find the resonant frequency (units: rad/s)

answer:
R = V/I = 155/4.3 = 3.6A

XL = Vmax / Imax = 155/36 = 4.3

XL = wL
w = 4.3/11E-3 = 391rad/s

b) find Irms at resonance when w = 7.6E3 rad/s

XL = 7.6E3 * 11E-3
= 83.6 ohm
XL = V/I
I = V/XL
= 155/83.6
= 1.85A

pls direct me if I am wrong... appreciate it... I've learned more in this forum than in school...

thanks
cseet
 
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  • #2
Hi all,
I reckon b) 1.85A is the Imax therefore it should be 1.85 / square root of 2 = 1.31A?
pls advise
cseet
 
  • #3
Resonant frequency is achieved when the reactances of the capacitor and induction coil are equal. The resistance of the resistor in this case doesn't matter, and neither do the maximum EMF or current.

[tex]X_L = X_C[/tex]
[tex]\omega L = \frac{1}{\omega C}[/tex]
[tex]\omega ^2 = \frac{1}{LC}[/tex]

I get a value of 5.6E3 rad/s.

As for the second part, I don't quite understand why it says "find Irms at resonance when w = 7.6E3 rad/s", because, as I just demonstrated, the circuit is only at resonance for ω = 5.6E3 rad/s. But, I will show you how to find I(rms) regardless, since you went about it the wrong way (you found the current through the coil alone, not the circuit as a whole). The overall 'resistance' of the circuit is Z, which is:

[tex]Z^2 = R^2 + (X_L - X_C)^2[/tex]

So the average current is:

[tex]I_{rms} = \frac{V_{rms}}{Z} = \frac{\frac{V_{max}}{\sqrt{2}}}{\sqrt{R^2 + (X_L - X_C)^2}}[/tex]

Where XL and XC both depend on \omega;.
 

1. What is the purpose of clarification in a physics problem?

The purpose of clarification in a physics problem is to ensure that all aspects of the problem are clearly understood and that there are no misunderstandings or ambiguities. This helps to prevent errors and confusion when solving the problem.

2. How do I know when I need clarification on a physics problem?

If you are unsure about any part of the problem or if you are struggling to understand the given information or the required steps to solve the problem, it is best to ask for clarification. It is always better to clarify any doubts before attempting to solve the problem.

3. Who should I ask for clarification on a physics problem?

You can ask your teacher, a classmate, or a tutor for clarification on a physics problem. It is important to seek help from someone who is knowledgeable and can provide you with a clear explanation.

4. How can I effectively communicate my need for clarification on a physics problem?

To effectively communicate your need for clarification, it is important to be specific about the part of the problem that you are struggling with. You can also provide an explanation of your thought process so far, so the person helping you can better understand where you are getting stuck.

5. Is it okay to ask for clarification multiple times on a physics problem?

Yes, it is completely okay to ask for clarification multiple times on a physics problem. It is better to have a clear understanding of the problem and the solution method rather than making mistakes and getting incorrect answers. Your teacher or tutor will be happy to assist you until you fully understand the problem.

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