How to find supply frequency of an AC circuit

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Homework Help Overview

The discussion revolves around determining the supply frequency in a parallel AC circuit that includes a resistor and a capacitor. The original poster presents their calculations and expresses confusion regarding the frequency value obtained.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to calculate the supply frequency using the voltage across the capacitor and the current through it, but questions the validity of their result. Participants raise concerns about the equations being used and suggest checking the relationships between voltage, current, and reactance.

Discussion Status

Participants are engaging with the original poster's calculations, providing feedback on the equations used and suggesting alternative approaches. There is an ongoing exploration of the correct method to find the frequency, with some guidance offered regarding the relationships between voltage and reactance.

Contextual Notes

There is a mention of potential confusion regarding the units of voltage and reactance, as well as the need for a proper equation to determine frequency. The original poster's calculations lead to an unexpectedly high frequency value, prompting further discussion.

Alan McMaster
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Homework Statement


[/B]
Parallel circuit consists of 100ohm resistor with 0.4A current, a 0.47uf capacitor with 0.177A current. Both connected across an AC supply, determine

Homework Equations


[/B]
The supply voltage
The supply frequency
Current drawn from supply
Power factor of the circuit
The Apparent power

The Attempt at a Solution


[/B]
The supply voltage is 40V.
Supply frequency is where I am stuck at the minute. I have VL=VC=XC

So VC=1/(2PiFC)
Substitute F for VC and I get VC=1/(2PiC*VC)
F= 1/(2Pi *0.47x10-6*40V)
Doing that equation I get 8465.69Hz which is crazy?

Thanks in advance Alan
 
Last edited by a moderator:
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Hello Alan, welcome to PF :)

Do the relevant equations look like equations to you ?

I take it the 40 V follows from I = V/R, so that qualifies as an equation and you have attempted a solution (and it's OK)

Perhaps the 0.177 and the 0.47 uF plus the 40 V can lead you to a frequency -- if you have a decent equation at hand, that is. Any idea ?


PS Check out the guidelines
 
Alan McMaster said:

Homework Statement



Parallel circuit consists of 100ohm resistor with 0.4A current, a 0.47uf capacitor with 0.177A current. Both connected across an AC supply, determine[/B]

Homework Equations



The supply voltage
The supply frequency
Current drawn from supply
Power factor of the circuit
The Apparent power[/B]

The Attempt at a Solution



The supply voltage is 40V.
Supply frequency is where I am stuck at the minute. I have VL=VC=XC

So VC=1/(2PiFC)
Substitute F for VC and I get VC=1/(2PiC*VC)
F= 1/(2Pi *0.47x10-6*40V)
Doing that equation I get 8465.69Hz which is crazy?
[/B]
Thanks in advance Alan
Hello Alan,

Welcome to Physics Forums.

Voltage and reactance are not the same thing (one has units of Volts and the other Ohms). You have the potential across the capacitor (40 V) and the current though it, so you can determine the reactance...
 
This is where I am at now, Xc=V/I which is 40V/0.177A=225.99

F= 1/(2Pi * 0.47x10-6 * 225.99)= 1498.41Hz
 
Well done
 
How to calculate frequency of AC signal?
 
Sanat Mishra said:
How to calculate frequency of AC signal?
Hello Sanat, :welcome:
Please start a new thread for this question and use the homework template.
 

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