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The electric charge of a macroscopic object is the sum of the electric charges of the particles that it is made up of. This charge is often small, because matter is made of atoms , and atoms typically have equal numbers of protons and electrons , in which case their charges cancel out, yielding a net charge of zero, thus making the atom neutral.
The charges must have a spherically symmetric distribution (e.g. be point charges, or a charged metal sphere). The charges must not overlap (e.g. they must be distinct point charges). The charges must be stationary with respect to a nonaccelerating frame of reference. The last of these is known as the electrostatic approximation. When movement ...
The electrons, the charge carriers in an electrical circuit, flow in the direction opposite that of the conventional electric current. The symbol for a battery in a circuit diagram The conventional direction of current, also known as conventional current , [ 10 ] [ 11 ] is arbitrarily defined as the direction in which positive charges flow.
where = is the distance of each charge from the test charge, which situated at the point , and () is the electric potential that would be at if the test charge were not present. If only two charges are present, the potential energy is Q 1 Q 2 / ( 4 π ε 0 r ) {\displaystyle Q_{1}Q_{2}/(4\pi \varepsilon _{0}r)} .
The electric field was formally defined as the force exerted per unit charge, but the concept of potential allows for a more useful and equivalent definition: the electric field is the local gradient of the electric potential. Usually expressed in volts per metre, the vector direction of the field is the line of greatest slope of potential, and ...
There are two recognized types of charge carriers in semiconductors. One is electrons, which carry a negative electric charge. In addition, it is convenient to treat the traveling vacancies in the valence band electron population as a second type of charge carrier, which carry a positive charge equal in magnitude to that of an electron. [12]
A point charge q in the electric field of another charge Q. The electrostatic potential energy, U E, of one point charge q at position r in the presence of a point charge Q, taking an infinite separation between the charges as the reference position, is:
Paul Dirac argued in 1931 that if magnetic monopoles exist, then electric charge must be quantized; however, it is unknown whether magnetic monopoles actually exist. [9] [10] It is currently unknown why isolatable particles are restricted to integer charges; much of the string theory landscape appears to admit fractional charges. [11] [12