Capacitor Question

Thread Starter

Nirvana

Joined Jan 18, 2005
58
Hi there I have been told that " When a capacitor stops charging there is no current flow" and I am not entirely sure what they mean exactly.
Do they mean that once the capacitor is fully charged, no current will flow through it any more. Or do they mean that no current will flow through the entire circuit. Also if there is no current flow does that mean that there will be no voltage either as I have been told " no voltage without current".

Please Help
 

Dave

Joined Nov 17, 2003
6,970
It is easiest to consider a capacitor under DC conditions.

Strictly speaking there is no current flow "through" a capacitor, since there is a dielectric, or insulator, sandwitched in the middle. When they say, "When a capacitor stops charging there is no current flow", they mean there is no current flow to one of the capacitor plates.

Think about when a capacitor is charging, charge is building up on one of the plates of the capacitor, this requires a movement of charge onto that plate, and the movement of charge is merely current flow. When the capacitor is fully charged, no more charge can gather on the plate and the current flow ceases.

As for voltage across a capacitor, well as the capacitor plate is charging the voltage across the capacitor (i.e. from plate to plate) is increasing. When the capacitor is full charged there is a fixed voltage across the capacitor.
 

tronicz18

Joined Jul 26, 2005
8
Originally posted by Nirvana@Aug 23 2005, 10:51 PM
Hi there I have been told that " When a capacitor stops charging there is no current flow" and I am not entirely sure what they mean exactly.
Do they mean that once the capacitor is fully charged, no current will flow through it any more. Or do they mean that no current will flow through the entire circuit. Also if there is no current flow does that mean that there will be no voltage either as I have been told " no voltage without current".

Please Help
[post=9834]Quoted post[/post]​
 

Dave

Joined Nov 17, 2003
6,970
I'm not sure what has happened to tronicz18's reply but here is his answer:

hi nirvana!

when a capacitor is charging It stores electrical charges untilthe voltage across it's terminal equals that of the source of EMF (electro motive force ) after this, no current will flow thru the capacitor again except after D capacitor is discharged
so, their is series capacitors in this case the resultant capacitance will reduce parallel capacitors has increased resultant capacitance mixed capacitors has the calculations broken to parallel & series & the resultant capacitance is calculated according to the final connetion of the mesh
Dave
 
When we connect a capacitor in a simple series RC network. Initialy voltage across the capacitor is 0v and current flow by formulat V/R.
Then instanteniously with respect to the time capacitor starts to charge and
current starts decreasing.
At 5RC time constant ther will be 0 current through the capacitor and capacitor
will be charged to the voltage equal to V battery volts.
If u connec Ammeter in series and Voltmeter across capacitor Ammeter will show 0A deflection and Voltmeter will show V volts.
 
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