| additive scalar quantity attributed to any particle and, generally, any system of them, to characterize its electromagnetic interactions NOTE 1 Electric charge is always an integral multiple of the elementary electric charge, except for quarks. The result may be positive, negative, or zero. NOTE 2 Due to additivity, electric charge for any system of particles is well defined as the sum of their charges. NOTE 3 Electric charge is subject to a conservation law. It is an invariant under Lorentz transformation, and thus not dependent on the choice of a reference frame. NOTE 4 The electric current through a surface is the time derivative of the electric charge transferred through that surface. NOTE 5 The coherent SI unit of electric charge is coulomb, C. The unit ampere hour is used for electrolytic devices, such as storage batteries: 1 A∙h = 3,6 kC. NOTE 6 To denote the charge of a point object, q is often used.
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