CAPACITANCE
Capacitance is the ability of a device to store electric charge; the component that stores charge is called a capacitor. The simplest consist of two flat conducting plates separated by a small gap. The potential difference, or voltage, between the plates is proportional to the difference in the amount of the charge on the plates. Capacitance is the amount of charge that can be stored per unit of voltage. The unit for measuring capacitance is the farad (F), named for physicist Michael Faraday, and is defined as the capacity to store one coulomb of charge with an applied potential of one volt. One coulomb (C) is the amount of charge transferred by a current of one ampere in a second.
To maximise efficiency, capacitor plates are stacked in layers or wound in coils with a very small air gap between them. Dielectric materials – insulating materials that partially block the electric field between the plates – are often used within the air gap. This allows the plates to store more charge without arcing and shorting out.
Capacitors are often found in active electronic circuits that use oscillating electric signals, such as those in radios and audio equipment. They can charge and discharge nearly instantaneously, which allows them to be used to produce or filter certain frequencies in circuits. An oscillating signal can charge one plate of the capacitor while the other plate discharges, and then, when the current is reversed, it will charge the other plate while the first plate discharges.
In general, higher frequencies can pass through the capacitor, while lower frequencies are blocked. The size of the capacitor determines the cutoff frequency for which signals are blocked or allowed to pass. Combinations of capacitors can be used to filter selected frequencies within a specified range.
Stronger supercapacitors are manufactured using nanotechnology to create super-thin layers of materials, such as graphene, that achieve capacities that are 10 to
100 times that of conventional capacitors of the same size. However, they have much slower response times than conventional dielectric capacitors, so they can’t be used in active circuits.