Need some help with Physics

[PistonFan531]

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Do you guys think you could help me out with a few physics problems? I've been stuck on these forever now and I'm really getting annoyed that I am continuing to get wrong answers.

1. For a particular RLC series circuit, the capacitive reactance is 12 ohms, the inductive reactance is 8.5 ohms, and the maximum voltage across the 25 ohms resistor is 8.7 V.

a. what is the impedence of the circuit?

b. What is the maximum voltage across the circuit?

2. An RLC circuit is connected to a 240-V rms power supply at a frequency of 2.5 kHz. The elements in the circuit have the following values: R= 2 ohms, C= .26E-6 F, and L= 30 mH.

a. What is the impedence of the circuit?

b. What is the rms current?

c. What are the rms voltages across each circuit element?

VR= ?
VC= ?
VL= ?

 

[enjoydrywax]

Thank god I am going to medical school and no longer have to deal with this stuff.. and I am an engineer too.

Hey post the answers so I see if my prelim work is correct

 

[TupacalipseT96]

pretty sure for these, you just need to plug those values into the correct equation and solve for the unknown. Do it in the right order and you're home free. What those equations are and any other detail, I cannot say because I have promptly forgotten all the details of EM Physics.

Compile a list of all the equations relating to RLC and it should be pretty obvious...those look like pretty standard questions for RLC circuits. Unless your text book is complete garbage, I bet you could even find a sample problem that does each one of those.

 

[airplanes]

I hate physics with a passion. Thank the lord I will be done with it forever after my final next Wednesday. I haven't been able to comprehend anything this term as calc-based physics took a severe derailment to engineer-ville.

please let me pass please let me passss

 

[nwilkes]

For a particular RLC series circuit, the capacitive reactance is 12 ohms, the inductive reactance is 8.5 ohms, and the maximum voltage across the 25 ohms resistor is 8.7 V.

a. what is the impedence of the circuit?

Z = sqrt of [R^2 - (Xl - Xc)]

Plug 'n' chug. Z is impedence, R is the resistance (square it). Xl is the inductive reactance, and Xc is the capacitive reactance.

b. What is the maximum voltage across the circuit?

Vrmax = (Imax)(R) --> Imax = Vrmax/R

So, Vmax = (Imax)(Z)



2. An RLC circuit is connected to a 240-V rms power supply at a frequency of 2.5 kHz. The elements in the circuit have the following values: R= 2 ohms, C= .26E-6 F, and L= 30 mH.

a. What is the impedence of the circuit?

See equation above.

b. What is the rms current?

The current given is the peak current....look in your book for the conversion factor. You can derive it, though, just for the fun of it: i^2 varies according to sin^2 ( (2)(pi)(f)(t) ) so, i average is half (Imax)^2.

c. What are the rms voltages across each circuit element?

Since you have (after part b) Irms, you can solve for Vr,rms, Vc,rms, and Vl,rms because: Vr,rms = (Irms)(R), etc.

VR= ?
VC= ?
VL= ?

 

[PistonFan531]

For a particular RLC series circuit, the capacitive reactance is 12 ohms, the inductive reactance is 8.5 ohms, and the maximum voltage across the 25 ohms resistor is 8.7 V.

a. what is the impedence of the circuit?

Z = sqrt of [R^2 - (Xl - Xc)]

Plug 'n' chug. Z is impedence, R is the resistance (square it). Xl is the inductive reactance, and Xc is the capacitive reactance.

b. What is the maximum voltage across the circuit?

Vrmax = (Imax)(R) --> Imax = Vrmax/R

So, Vmax = (Imax)(Z)



2. An RLC circuit is connected to a 240-V rms power supply at a frequency of 2.5 kHz. The elements in the circuit have the following values: R= 2 ohms, C= .26E-6 F, and L= 30 mH.

a. What is the impedence of the circuit?

See equation above.

b. What is the rms current?

The current given is the peak current....look in your book for the conversion factor. You can derive it, though, just for the fun of it: i^2 varies according to sin^2 ( (2)(pi)(f)(t) ) so, i average is half (Imax)^2.

c. What are the rms voltages across each circuit element?

Since you have (after part b) Irms, you can solve for Vr,rms, Vc,rms, and Vl,rms because: Vr,rms = (Irms)(R), etc.

VR= ?
VC= ?
VL= ?

For 1a I'm getting 618.5 as my answer. (and sorry the inductive reactance is 18.5 not 8.5 ohms). And this is not the correct answer. 25 is the resistor, right?

And another question: what is imax?

 

[nwilkes]

Sorry, just realized I mis-typed - Z should be the sqrt of [R^2 + (xl-Xc)^2] not of (R^2 - (xl-xc)^2). (I do remember trig, I really do! 🙂 ) ....the correct equation is in your text I'm sure, if you want to check.


When I do this, I get an answer of around 24 ohms. Does that sound better? I think you might've forgotten to take the square root (not to mention my little typo).


Imax is the maximum current in your RLC circuit. (Remember, the voltage of the source is AC - it's alternating, not direct current, so it's going to follow a sinusoid wave pattern. The maximum current, obviously, is the "peak" current - the peak of the sine wave. Your rms current is the average current through the circuit. )

And, yes, 25 ohms is the value of your resistor. The max voltage across it is 8.7 V.

 

[Jolie South]

Asking for others to help solve specific homework problems is not permitted. Closing thread.