Capacitors are devices used to store electric charge and usually involve conducting plates separated by an insulator. (One plate is positive while the other is negative.)
When the capacitor is connected to a battery, electrons flow from the negative terminal to plate
Capacitors are widely used in electronic circuits to block the flow of direct current (D.C) while allowing alternating current(A.C) to pass, to filter out interference, to smooth the output of power supplies, and for many other purposes.
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related video from http://ec.europa.eu/research/mariecurieactions/
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