Capacitors - Technical MCQs

Q1:

When is a capacitor fully charged?

A when the voltage across its plates is of the voltage from ground to one of its plates

B when the current through the capacitor is the same as when the capacitor is discharged

C when the voltage across the plates is 0.707 of the input voltage

D when the current through the capacitor is directly proportional to the area of the plates

ANS:B - when the current through the capacitor is the same as when the capacitor is discharged

Option B is correct because a capacitor will be fully charged if the current that it discharges has the same value as the current from the source that charged it. For example a voltage source has a value of 25V with current equals to 1 Ampere. If the source is turned off, the capacitor will discharge, if the current that the capacitor discharges has a value of 1 Ampere then we can assume that is has been fully charged since a current of 1 ampere would indicate that the value of charge stored in the capacitor is 25V.