When do we say that the capacitors are said to be discharging?

Question

When do we say that the capacitors are said to be discharging?

Answer 1

Imagine a nightclub with 2 entrance doors one on the left and one on the right with 20ft of pavement (sidewalk) between them. 100 people are waiting to enter but dont know which door will open. whilst waiting they are spread out evenly in the gap between the doors. (Equilibrium) This state is similar to a capacitor that is not charged. The electrons are evenly distributed throughout the circuit.

A light appears at the left door and all the people rush to that door pushing against the glass and each other hoping to gain entrance. The right door has no-one in the area.

This is the effect of charging a capacitor. The 2 doors represent the plates of the capacitor the people represent the electrons in the circuit.

Lets imagine the people are still pushing at the left door and a third door is placed on the pavement between the original doors.

A light now goes on at the right door and people believe that door is opening so they move towards that door but to get there they must pass through the door on the pavement (sidewalk). It only allows one person per minute to pass through thus limiting the flow of people. When the number of people on each side of the middle door is equal then the flow stops as they still don't know which door will open. Overall there are an equal number of people waiting at each of the left and right doors (equilibrium or uncharged state.)

This is what happens when a resistor is connected across the capacitor the electrons have a path through the resistor back to equilibrium

So when a capacitor is discharging the electrons built up on the negative plate during charging flow back to a zero charged state IE equally distributed throughout the circuit.

Taking the same scenario imagine the club having a bit of fun switching on the left hand door light then the right hand door light alternately. The people will run from one door to the other back and forth but never getting into the club.

This is the capacitor in an AC circuit the doors represent the plates the inside of the club the insulator (dielectric) and the people represent the electrons flowing one way and then the other as AC current.      

Answer 2

It is easier to think of this in terms of potential.

A charged capacitor has a potential difference.  For example, imagine a capacitor, uncharged -- the two plates of the capacitor have the same potential.  Then, if you hook one end of a capacitor to the positive end of a 1.5V battery, and the other end to the negative end of that battery, the capacitor will begin "charging" -- the potential difference between the two plates will start to increase until it reaches 1.5V, at which point the capacitor is fully charged.  Then, if disconnected from the battery, the capacitor will begin "discharging" as the potential difference decreases from 1.5V to zero (no charge).

A good way to determine whether a capacitor is charging or discharging is to ask yourself "Is the potential difference across the plates increasing, or decreasing?"  A discharging capacitor has a decreasing potential difference.

Answer 3

That means the capacitors are losing charge. If a capacitor is charged up by hooking it up to a battery and then disconnecting it, it can be discharged by hooking it up to a resistor.