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I know that capacitors can be charged to work like a battery . But I wanted to know whether we can charge a capacitor while it is in use ( given that the current supplied to it is more than what it has to give in a circuit ).

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    $\begingroup$ That is exactly what happens in the smoothing circuit of a dc power supply. en.wikipedia.org/wiki/Ripple_%28electrical%29 $\endgroup$
    – Farcher
    May 17 '16 at 10:37
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    $\begingroup$ Would Electrical Engineering be a better home for this question? $\endgroup$
    – Qmechanic
    May 17 '16 at 10:40
  • $\begingroup$ ... or in an oscillator. More often than not, they are used while charging or discharging. Your parenthetical remark is irrelevant. $\endgroup$
    – garyp
    May 17 '16 at 10:43
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But I wanted to know whether we can charge a capacitor while it is in use

If, by "while it is in use", you mean while the capacitor is discharging, i.e., energy is flowing out of the capacitor to some load, then the answer is no since, by definition, if a capacitor is charging, energy is flowing into the capacitor.

Put another way, a capacitor cannot be both charging and discharging at the same time. Either, the energy stored in a capacitor is increasing, unchanging, or decreasing.

given that the current supplied to it is more than what it has to give in a circuit

If the capacitor is charging, it is not 'giving' current to a circuit; whatever is supplying current to the capacitor is also supplying current to the circuit.


From a comment:

I'm talking about a power supply charging the capacitor and the same capacitor supplying power to a load simultaneously. Is it possible?

(my emphasis)

To recapitulate what I wrote above, no, it is not possible.

If the power supply is charging the capacitor, the capacitor is not supplying power to the load simultaneously.

Instead, the power supply is supplying power to both the load and the capacitor simultaneously.

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    $\begingroup$ From a real world perspective this is incorrect, and your mistake may be in terminology. This is not charging vs discharging. In reality, many circuits allow the capacitor to charge while the device is in use. Oscillators, power supplies, emergency backup power etc. I suggest a migration to Electronics, as their answers are likely to be more relevant to the OP than this answer, which is technically correct from an academic Physics point of view. $\endgroup$
    – Rory Alsop
    May 17 '16 at 11:10
  • $\begingroup$ @RoryAlsop, the OP clearly begins the question with the comparison of a capacitor as an energy storage device 'like a battery'. I clearly begin my answer by establishing the context of using the capacitor as a source 'like a battery'. $\endgroup$ May 17 '16 at 11:21
  • $\begingroup$ I'm talking about a power supply charging the capacitor and the same capacitor supplying power to a load simultaneously. Is it possible? $\endgroup$
    – Yash Singh
    May 17 '16 at 11:25
  • $\begingroup$ @YashSingh, it is not possible. $\endgroup$ May 17 '16 at 11:26
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    $\begingroup$ Hash - for the purposes of your circuit, if you are supplying power and supplying power to a load, as long as your supply is greater than that load, then you can be charging the capacitor at the same time. This is why I say Alfred's answer is academically correct, but not necessarily useful in reality. Depends what you want from your circuit. If you want to know that when you unplug power your capacitor is fully charged, then you can do that, yes. $\endgroup$
    – Rory Alsop
    May 17 '16 at 11:50
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A capacitor is storing an electrical charge. Simply speaking: If the voltage across the capacitor rises, then the charge will increase and if the voltage decreases charge will be flowing out. In any normal circuit, this happens all the time in both directions.

Obviously, it can't happen simultaneously since the voltage either decreases or increase but not both at the same time. However, the transitions between these two states can be arbitrarily fast, they are not different mode of operations, they are simply different states for the circuit.

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