Capacitance and the relationship between voltage and stored charge
A capacitor stores electrical energy by separating charges: positive charges accumulate on one plate and negative charges on the other. Capacitance measures how much charge a device can hold per unit voltage. A larger plate area increases capacitance, as does bringing the plates closer together. The energy stored depends on the capacitance and the applied voltage, following the formula E equals one-half times C times V squared. This quadratic dependence on voltage means doubling the voltage quadruples the stored energy, explaining why high-voltage capacitors store vastly more energy than low-voltage ones of the same physical size.
Applications from power electronics to imaging
Capacitors serve as fast energy storage in electronic devices. Camera flashes rely on capacitors that charge slowly from batteries then discharge almost instantaneously to produce the bright pulse. Power electronics use capacitors to stabilize voltage supplies by absorbing voltage spikes and smoothing ripples. Touchscreens detect fingers because the human body acts as a capacitor, changing the capacitance at each contact point. Supercapacitors extend the principle to store enough energy to power devices for seconds or minutes, finding use in emergency lighting and hybrid vehicles where rapid charge and discharge cycles are essential.