Equivalent capacitance, circular arrangement

In summary: A and B is the capacitance of the single capacitor you replace the whole network between A and B with, so as nothing changes in the voltages and charges in the external network.In summary, DaveMirrors reversed front to back, not top to bottom. Otherwise you'd be looking at your feet in the mirror rather than your eyes.
  • #36
gracy said:
Should not I fix terminals at c and d?like this

View attachment 92900
You can if you want to. It doesn't change the circuit operation in any way if you don't connect anything to the new terminals. Open terminals won't pass any current.
 
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  • #37
What connection terminal means?
 
  • #38
gracy said:
What connection terminal means?
I think it provides a point of connection to external circuits.So there should be some supplied voltage.
 
  • #39
gracy said:
I think it provides a point of connection to external circuits.So there should be some supplied voltage.
There can be output voltage also.
 
  • #40
Gracy, have you constructed circuits and measured voltage at various places in the circuit?
 
  • #41
gneill said:
You can if you want to. It doesn't change the circuit operation in any way if you don't connect anything to the new terminals.
don't connect anything means?not even voltage source?
 
  • #42
gracy said:
I think it provides a point of connection to external circuits.So there should be some supplied voltage.
Not necessarily. You don't have to connect anything if you don't want to. Sometimes terminals are just provided for test points to make it convenient to connect test equipment like voltmeters.

Unless you connect something to a circuit it doesn't affect the circuit.

In many instances "output terminals" are drawn in order to draw your attention to where you should consider the circuit output to be. They don't affect the operation of the circuit just by being there.
 
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  • #43
gracy said:
don't connect anything means?not even voltage source?
Right.

I mean, you could connect a voltage source there or anywhere else you wanted for that matter. But then you'd be changing the circuit and creating a different problem to analyze.
 
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  • #44
gneill said:
When the problem named and labelled the two nodes A and B between which you are to determine the capacitance, it effectively implied connection terminals for the circuit.
In such cases we should not apply voltage ?As we can see you did not apply voltage but made A and B connection terminals there when the question asked to find equivalent potential between A and B

fig1-png.92577.png


Right?
 
  • #45
gracy said:
In such cases we should not apply voltage ?As we can see you did not apply voltage there when the question asked to find equivalent potential between A and B
You don't have to apply anything if the terminals are just serving as labels to identify certain nodes or specify a point of view (way of looking at the circuit).

The problem did not say to apply a voltage across AB. So don't.
 
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  • #46
gracy said:
If 100 volts of potential difference is applied between a and b in the circuit .Find the potential difference between c and d.
In this question I should apply voltage i.e 100 volts in between A and B but no voltage in between C AND D Because it would be wrong.Right?
 
  • #47
gracy said:
In this question I should apply voltage i.e 100 volts in between A and B but no voltage in between C AND D Because it would be wrong.Right?
Like this!(sorry capacitor and voltage source symbols look alike)
ki.png


Here C1 and C2 are not in series ,right?
 
  • #48
gracy said:
Here C1 and C2 are not in series ,right?
Right.
 
  • #49
please answer my #46
 
  • #50
Is current direction correct?
From positive terminal of battery to the rest of the circuit.
direction.png
 
  • #51
gracy said:
In this question I should apply voltage i.e 100 volts in between A and B but no voltage in between C AND D Because it would be wrong.Right?
Right. It would be wrong for the problem that you posed to apply another source between C and D. It would change the circuit and create a different problem.
 
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  • #52
gracy said:
please answer my #46
That's right too. Here, 100V is input and Vcd is the output voltage.
 
  • #53
gracy said:
Is current direction correct?
From positive terminal of battery to the rest of the circuit.
View attachment 92905
Correct conventionally.
 
  • #54
gracy said:
Is current direction correct?
From positive terminal of battery
View attachment 92905
Your indicated currents look fine for the instant that the circuit is first assembled. Since there are no resistances in the circuit it will reach steady-state essentially instantaneously though, and all current flow will cease leaving the capacitors with some charge values.
 
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  • #55
gneill said:
all current flow will cease leaving the capacitors with some charge values. [/QUOTE]

I did not understand.

gneill said:
Since there are no resistances

capacitors have resistance,right?
 
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  • #56
Capacitor 'plates' have resistance, which is negligible since they are metallic.
 
  • #57
Ideal components that aren't specifically resistances are considered to have no resistance. In a circuit diagram, unless otherwise specified, components are taken to be ideal. Capacitors, inductors, and wires are considered to be ideal components, and so have no inherent resistance.
 
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  • #58
gneill said:
and all current flow will cease leaving the capacitors with some charge values.
I don't understand.
 
  • #59
gracy said:
I don't understand.
Once the capacitors are charged, the currents will cease. This will happen really very fast as there is no resistance in the circuit.
 
  • #60
batteries/voltage source have resistance,right?
 
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  • #61
gracy said:
batteries/voltage source has resistance,right?
Not ideal ones. An ideal battery would be a pure voltage source, no resistance. Ideal components are perfect representations of the quality that they are specified to be. An ideal capacitor is capacitance only. An ideal inductor is inductance only. An ideal resistor is resistance only. An ideal voltage source is a voltage source only.

Real world components, being made of imperfect real-world materials, will exhibit some mix of traits in addition to the one they are designed for. So a real capacitor, for instance, may have some very tiny resistance and inductance associated with its wire leads. Usually these imperfections are small enough to ignore for practical design and operational purposes. When they are not negligible for a given component or circuit situation you will be told so in the problem statement.
 
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  • #62
gracy said:
In such cases we should not apply voltage ?As we can see you did not apply voltage but made A and B connection terminals there when the question asked to find equivalent potential between A and B

To find a voltage or potential difference you would connect a voltmeter.

To apply a voltage or potential difference you would connect a battery.
 

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