Reed Relays and
Electronics India Limited
Manufacturer of Reed Switches, Reed Sensors and Reed-based products
Reed Relays and Electronics India Limited Incorporated in 1971


Capacitance is the ability of a system to store an electric charge, and is expressed in Farads. Reed Switch control circuits should be designed to ensure that stray capacitance does not discharge across the reed switch during the time of closure as this will degrade the contact and reduce life.

Capacitance (Wikipedia)

Common symbols
SI unit farad
Other units
μF, nF, pF
In SI base units F = A2 s4 kg−1 m−2
Derivations from
other quantities
C = charge / voltage
Dimension M−1L−2T4I2

Capacitance is the ratio of the change in an electric charge in a system to the corresponding change in its electric potential. There are two closely related notions of capacitance: self capacitance and mutual capacitance. Any object that can be electrically charged exhibits self capacitance. A material with a large self capacitance holds more electric charge at a given voltage than one with low capacitance. The notion of mutual capacitance is particularly important for understanding the operations of the capacitor, one of the three elementary linear electronic components (along with resistors and inductors).

The capacitance is a function only of the geometry of the design (e.g. area of the plates and the distance between them) and the permittivity of the dielectric material between the plates of the capacitor. For many dielectric materials, the permittivity and thus the capacitance, is independent of the potential difference between the conductors and the total charge on them.

The SI unit of capacitance is the farad (symbol: F), named after the English physicist Michael Faraday. A 1 farad capacitor, when charged with 1 coulomb of electrical charge, has a potential difference of 1 volt between its plates. The reciprocal of capacitance is called elastance.

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