![]() microscopic descriptionĬurrent is the flow of charged particles. In fluid mechanics ρ stands for mass density, while in electric current it represents charge density. The exact same expression applies to electric current with the symbol ρ changing meaning between contexts. This product is the quantity that stays constant in the mass continuity equation. Readers familiar with fluid mechanics might recognize the right side of this equation if it was written a bit differently. The two equations are equivalent in magnitude as shown below. Well… actually, it's because current density is defined as the product of charge density and velocity for any location in space… ⎡ĭespite being the ratio of two scalar quantities, current density is a vector. The unit of current density is the ampère per square meter, which has no special name. The ratio of current to area for a given surface is known as the current density. And the reason is… because it is.īut wait, it gets weirder. Current is not a vector quantity, despite my well-developed sense of scientific intuition. When I visualize current, I see things moving. For those who like coinceidences, this is about the same as ten micromoles. I'll write the first 19 digits, which is the most I can possibly write (since arbitrary fractions of the elementary charge don't exist).Īnd then I'll write it again with a more reasonable number of digits so it's easier to read.Ī current of one ampere is then the transfer of approximately 6.2415 × 10 18 elementary charges per second. ![]() The number of elementary charges in a coulomb would be the reciprocal of this number - a repeating decimal with a period of 778,716 digits. The elementary charge is defined to be exactly… Since charge is measured in coulombs and time is measured in seconds, an ampère is the same as a coulomb per second. Ampère refers to a physicist, while ampère (or ampere or amp) refers to a unit. Just don't use a capital "A" at the beginning. I have no problem with either of these spellings. In written languages without accented letters (namely English) it has become customary to write the unit as ampere and, in informal communication, to shorten the word to amp. The unit of current is the ampère, which is named for the French scientist André-Marie Ampère (1775–1836). The phrase "current through a toaster" surely refers to the flow of electrons through the heating element and not the flow of slices of bread through the slots.Īs with all quantities defined as a rate, there are two ways to write the definition of electric current - average current for those who claim ignorance of calculus… I =Īnd instantaneous current for those with no fear of calculus… I = The adjective "electric" is implied by the context of the situation being described. ![]() Despite referring to many different things, the word current is often used by itself instead of the longer, more formal "electric current". ![]() Electric current is defined as the rate at which charge flows through a surface (the cross section of a wire, for example). ![]()
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