What’s a Coulomb?

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A coulomb is a unit of electric charge, defined as the charge flowing with a constant current of one ampere for one second. It is useful in electrochemistry and physics. Charge flow or coulombs are important for paying electric bills. Electrons carry a charge and move when a potential or voltage is applied. Robert Millikan won the Nobel Prize for measuring the charge of an electron. Coulombs are used in electrochemistry and physics calculations.

A coulomb is a measure of electric charge and is defined as the charge flowing with a constant current of one ampere (1 ampere) during one second. The charge can be positive or negative. It is equivalent to 6.241 x 1018 electrons. The idea of ​​a coulomb is useful in electrochemistry and physics.
The properties of electricity are often compared to the physics of water in pipes or rivers. In this analogy, amperes, or amperage, are the velocity of water flow, and the coulomb is the amount of water transported during a given period of time. In everyday circumstances, most people are concerned with the voltage required by a fixture or the wattage of a replacement bulb. The actual charge flow or coulombs used are only important when it’s time to pay the electric bill.

An electric charge is not the same thing as an electron. An electron is a subatomic particle that carries a charge. In a piece of metal, the electrons are held in place rather loosely by protons, the positively charged nucleus of the atom. Once a potential or voltage is applied, the electrons move uniformly and charge is transferred as long as there is a potential difference between the ends of the metal, much like a river requires a vertical drop to flow.

Since the charge of one coulomb is equivalent to the sum of the charges of 6.241 x 1018 electrons, the charge of one electron is the inverse: 1 divided by 6.241 x 1018 electrons per coulomb. The charge on an electron is 1.602 x 10-19 coulombs. Robert Millikan won the Nobel Prize in 1923 for his work on measuring the charge of an electron.

The most familiar charge transfer occurs in a household electrical circuit. A metal conductor, usually copper wire, is used to transfer electricity from the household wire to a light. When a light switch is turned on, light appears instantly. This happens because the charge is actually moving faster than the electrons. It is also moving in the opposite direction.

Some solids transfer charges such as positively charged protons. Sometimes, the charge carriers of these solids are described as electron holes, or where the electrons should be. Semiconductors used in electronics are often made from materials that carry a positive charge. In these materials, the charge moves in the same direction as the charge carriers. Electrolyte solutions, solutions of dissolved minerals or other substances, carry charges in two directions, as negatively charged ions will travel in one direction and positively charged ions will travel in the opposite.

Coulombs are used in calculations involving electrochemistry and by physicists who study electricity and magnetism. A common high school chemistry problem will ask how much metal is deposited on a substrate in a metal plating bath, given the amperage and duration of the current applied. A physics problem using coulombs could concern the efficiency of a photovoltaic panel, which converts photon energy into electricity.

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