<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field . There are two types of electric charges: positive and negative (commonly carried by protons and electrons respectively). Like charges repel and unlike attract . An absence of net charge is referred to as neutral . An object is negatively charged if it has an excess of electrons, and is otherwise positively charged or uncharged . The SI derived unit of electric charge is the coulomb (C). In electrical engineering, it is also common to use the ampere - hour (Ah), and, in chemistry, it is common to use the elementary charge (e) as a unit . The symbol Q often denotes charge . Early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that don't require consideration of quantum effects . </P> <P> The electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction . Electrically charged matter is influenced by, and produces, electromagnetic fields . The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the four fundamental forces (See also: magnetic field). </P>

Where do the two kinds of charges come from
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