# Capacitor Question

Discussion in 'General Electronics Chat' started by Nirvana, Aug 23, 2005.

1. ### Nirvana Thread Starter Well-Known Member

Jan 18, 2005
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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".

2. ### Dave Retired Moderator

Nov 17, 2003
6,960
144
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.

Jul 26, 2005
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4. ### Dave Retired Moderator

Nov 17, 2003
6,960
144
I'm not sure what has happened to tronicz18's reply but here is his answer:

Dave

5. ### PROBLEM_SOLVER New Member

Aug 25, 2005
1
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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.