Find c1 & c3 Given Vb, Vc, Vd, It, Xct Values

  • Thread starter Thread starter harrypotter
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around finding the unknown capacitance values c1 and c3 in a circuit, given certain known values including voltages, total current, and capacitive reactance. The context is primarily homework-related, focusing on the application of capacitive reactance in AC circuits.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses uncertainty about which equations to use for calculating c1 and c3, indicating a lack of clarity on the problem.
  • Another participant notes that capacitive reactance varies with frequency and questions whether the frequency of the AC source is known, suggesting that this information is necessary to proceed.
  • There is a discussion about the need to determine the frequency to relate the given Xc values to capacitance values, with one participant indicating confusion about how to find this frequency.
  • One participant points out that if all known values were capacitances, the frequency would not matter, but since only some values are given as Xc, frequency is crucial.
  • Several participants express confusion about the problem, with one asking for help in solving it and another questioning the units of the given Xc value for c4.
  • There is a mention of two loops and two unknowns in the circuit, with a participant suggesting that the total reactance and current must be considered in relation to the voltage source.
  • Participants discuss the relationship between voltage, current, and reactance, but the specifics of the equations to be used remain unclear.

Areas of Agreement / Disagreement

Participants generally agree that the frequency of the AC source is a critical missing piece of information needed to solve the problem. However, there is no consensus on how to proceed with the calculations or the specific values of the unknown capacitances.

Contextual Notes

There are limitations in the discussion regarding the missing frequency information and the unclear units for the given Xc values. The relationship between the known and unknown variables is not fully resolved, and participants express varying levels of understanding of the circuit's configuration.

harrypotter
Messages
6
Reaction score
0

Homework Statement



find c1 & c3

known values:

c2= .01uF
Xc= 2.34k
c5= .047uF
c6= .033uF

given these values:

Vb 21.91v

Vc 17.51v

Vd 14.48v

It 1.76mA

Xct 28.34k ohms

http://i216.photobucket.com/albums/cc193/harrypotter33/Untitled-1.jpg

Homework Equations



im not sure which equation to use

The Attempt at a Solution



im not sure what to do

i don't know if I am in the right forum

thanks
 
Last edited by a moderator:
Physics news on Phys.org
Capacitive reactance varies with frequency, so you need to know what frequency is being used by the AC source. Otherwise, you cannot mix Xc impedances and C capacitances in the same capacitive voltage divider equation. Do you have some way to determine the frequency? Like, are you given both Xc and C for any of the caps (I don't see that)?

Welcome to the PF, BTW. And yes, you picked the right subforum for your question.
 
thank you for the reply. the Xc for c4 is 2.34k. so, i need to figure out the frequency first? but how do i figure this out?
 
I'm not tracking the whole problem very well, but it looks like they have given you a mixture of capacitances and Xc impedance values, and are asking you to calculate two unknown capacitance values. If you had all the known capacitors as capacitance values, then the frequency of excitation would not matter, and you could just calculate the unknown cap values using the relative impedances. But if you are only given information about a couple of the capacitor positions as Xc values, then you need to know the frequency of excitation that the Xc is given for. You would use the frequency to get back to the capacitor values for those positions.
 
this is more confusing than trying to remember the logic gates. anyone want to try and solve this for me please? :)
 
the Xc for c4 is 2.34k
but what is the capacitance of c4?

In the OP one states c4 = 2.34k. Are the units [itex]\mu[/itex]F, which would be an impressive capacitor, or pF?

Capacitive reactance, Xc = 1/([itex]\omega[/itex]C).
 
Astronuc said:
but what is the capacitance of c4?

In the OP one states c4 = 2.34k. Are the units [itex]\mu[/itex]F, which would be an impressive capacitor, or pF?

Capacitive reactance, Xc = 1/([itex]\omega[/itex]C).

oh sorry, the capacitance of c4 wasnt given. but was given an Xc of 2.34k instead
 
Well there are two loops and two unknowns, C1 and C3.

Take the potenials with respect to ground below the voltage source.

I take it the Xt is the total reactance, and It is the total current, which must pass through the voltage and those capacitors which are in series with the voltage source.

What can one say about VA, It and Xt?
 
...Va, It, Xt = Vs ?
 
  • #10
harrypotter said:
...Va, It, Xt = Vs ?
Well Va = Vs, assuming the ground reference is at the bottom left of the figure, i.e. inlet to source.

It must go through C1, C5 and C6.

It*XC6 is related to VE.

Write some equations.
 
  • #11
edit: nm
 
Last edited:

Similar threads

Find the Voltage in the parallel resistor-capacitor circuit
  • · Replies 31 ·
2
Replies
31
Views
4K
Finding the Maximum Fan-Out of a distribution network
  • · Replies 1 ·
Replies
1
Views
2K
What is the value of C2 in the given circuit with capacitors C1, C3, and C4?
  • · Replies 11 ·
Replies
11
Views
5K
LC Circtuit finding Q across an element for given time
  • · Replies 2 ·
Replies
2
Views
9K