Coulomb
The coulomb is the standard unit of electric charge. One coulomb is defined as the amount of charge carried by one ampere of current in one second. One coulomb can also be defined as the amount of charge needed to create one volt of potential difference in a one farad capacitor. The symbol for the coulomb is an uppercase C.
History of the Coulomb
The coulomb was defined at an international conference in 1881, and is named after Charles-Augustin de Coulomb (1736-1806), a French physicist. He discovered Coulomb’s law which defines electrostatic force. The ampere was originally derived from the coulomb, until it was changed to a base unit itself.
Measuring Coulombs
Electric charge is measured with an electrometer which is a device that measures charge directly, unlike an electroscope which only measures relative charge. Older electrometers used valves but modern versions are solid-state, using field effect transistors that change their output based on the strength of the surrounding electric field.
Other Units
Electric charge density is expressed as the number of coulombs per cubic meter. Exposure to radiation, particularly x-rays and gamma rays, is often expressed as the coulombs of charge absorbed per kilogram of matter.
The coulomb is a large value, one ampere-hour of current transfers only 3600 coulombs of charge, so common values are measured in millicoulombs (one thousandth), nanocoulombs (one millionth), and picocoulombs (one billionth). Other units of electric charge that are sometimes used are the abcoluomb and the statcoulomb.
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- Amp (Ampere)
The ampere, amp for short, is the standard unit of electrical current. It is defined as the current required to produce a certain force between two parallel and infinitely long wires separated by one meter. According to Ohm’s law, one ampere of current is produced when one volt of potential difference exists across a conductor [...]...
- Farad
A farad is the standard unit of capacitance. It is defined as the capacitance required to create one coulomb of static charge for every volt of potential difference. Another definition is the capacitance that would change it's potential difference by one volt if one ampere of current flowed for one second. History of the Farad [...]...
- Dielectric
A dielectric is a material that restricts the flow of current. Dielectrics are defined by their dielectric constant, current leakage, and breakdown voltage. They are mainly used in capacitors, allowing charge to build up on the conductive plates. An insulator is a dielectric than can withstand a high electric field without letting current flow through [...]...
- Watt
A watt is a standard unit of power. It is equal to one joule of energy per second. For electrical power, one watt is equal to one ampere of current per second. History of Watt A watt was formally defined at an international conference in 1889. It is named after James Watt (1736-1819), a Scottish [...]...
- Volt
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