<P> Electric charges create an electric field, if they are moving they also generate a magnetic field . The combination of the electric and magnetic field is called the electromagnetic field, and its interaction with charges is the source of the electromagnetic force, which is one of the four fundamental forces in physics . The study of charged particles, and how their interactions are mediated by photons, is called quantum electrodynamics . </P> <P> The SI derived unit of electric charge is the coulomb (C). In electrical engineering, it is also common to use the ampere - hour (Ah); in physics and chemistry, it is common to use the elementary charge (e as a unit). Chemistry also uses the Faraday constant as the charge on a mole of electrons . The symbol Q often denotes charge . </P> <P> Charge is the fundamental property of forms of matter that exhibit electrostatic attraction or repulsion in the presence of other matter . Electric charge is a characteristic property of many subatomic particles . The charges of free - standing particles are integer multiples of the elementary charge e; we say that electric charge is quantized . Michael Faraday, in his electrolysis experiments, was the first to note the discrete nature of electric charge . Robert Millikan's oil drop experiment demonstrated this fact directly, and measured the elementary charge . It has been discovered that one type of particle, quarks, have fractional charges of either − 1 / 3 or + 2 / 3, but it is believed they always occur in multiples of integral charge; free - standing quarks have never been observed . </P> <P> By convention, the charge of an electron is negative, − e, while that of a proton is positive, + e . Charged particles whose charges have the same sign repel one another, and particles whose charges have different signs attract . Coulomb's law quantifies the electrostatic force between two particles by asserting that the force is proportional to the product of their charges, and inversely proportional to the square of the distance between them . The charge of an antiparticle equals that of the corresponding particle, but with opposite sign . </P>

Does a nucleus have a positive or negative charge