JEE Main & Advanced Physics Electrostatics & Capacitance Capacitor or Condenser

(1) A capacitor is a device that stores electric energy. or A capacitor is a pair of two conductors of any shape, which are close to each other and have equal and opposite charge.

(2) The capacitance of a capacitor is defined as the magnitude of the charge Q on the positive plate divided by the magnitude of the potential difference V between the plates i.e.,  \[C=\frac{Q}{V}\]

(3) A capacitor get's charged when a battery is connected across the plates. Once capacitor get's fully charged, flow of charge carriers stops in the circuit and in this condition potential difference across the plates of capacitor is same as the potential difference across the terminals of battery.

(4) Net charge on a capacitor is always zero, but when we speak of the charge Q on a capacitor, we are referring to the magnitude of the charge on each plate.

(5) Energy stored : When a capacitor is charged by a voltage source (say battery) it stores the electric energy. If C  = Capacitance of capacitor; Q = Charge on capacitor and V = Potential difference across capacitor then energy stored in capacitor \[U=\frac{1}{2}C{{V}^{2}}=\frac{1}{2}QV=\frac{{{Q}^{2}}}{2C}\]

In charging capacitor by battery half the energy supplied is stored in the capacitor and remaining half energy (1/2 QV) is lost in the form of heat.