Electric charge

Electric charge is an intrinsic property of matter, just as mass is. It is both the source and the “target” of all electric interactions: two bodies attract or repel each other electrically only if they are charged. Unlike mass, though, charge presents a decisive novelty: it can come in two types, conventionally called positive and negative.

This duality of signs is what makes electricity so different from gravity. Charges of the same sign repel each other, charges of opposite sign attract; and since both signs exist, ordinary matter tends to be neutral, with as many positive charges as negative ones, so that its electric effects cancel out at a distance. It is this underlying neutrality that hides, in everyday life, a force that is actually enormously stronger than gravity.

Unit of measurement

Charge is measured in coulombs (C). In the International System it is a quantity derived from electric current.

At the microscopic level, charge is quantised: every charge observed in nature is an integer multiple of the elementary charge $e$, that of the electron (negative) and the proton (positive, of opposite value).

Elementary charge

$\ev{e = 1{.}6\cdot 10^{-19}\;\text{C}}$

The coulomb is thus a “large” unit: a single coulomb corresponds to about $6\cdot 10^{18}$ elementary charges. This is why, in real problems, the charges involved are often measured in microcoulombs ($\mu\text{C} = 10^{-6}\;\text{C}$) or nanocoulombs ($\text{nC} = 10^{-9}\;\text{C}$).

▶ What is Electric Charge? — The Science Asylum

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Topics: Electrostatics Concepts: Electric charge

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