Electric Current
Electric current is the flow of electric charge through a material. It is the rate at which electric charge flows past a point in a circuit. The flow of electric charge is typically carried by electrons, which are negatively charged particles.
The SI unit for current is the coulomb per second, or the ampere (A), which is an SI base unit:
1 ampere = 1A = 1 coulomb per second = 1 C/s.
Direction of Current
A current arrow is drawn in the direction in which positive charge carriers would move, even if the actual charge carriers are negative and move in the opposite direction. This convention was established early in the development of electrical theory, before the nature of electric charge was fully understood, and is still used today for consistency and convenience. We can use this convention because in most situations, the assumed motion of positive charge carriers in one direction has the same effect as the actual motion of negative charge carriers in the opposite direction.
In reality, electric current is the flow of negatively charged electrons through a conductor rather than the flow of positive charge. However, the direction of current flow is still defined as the direction that the positive charge would move, from the positive terminal of a battery or power source, through the circuit, and back to the negative terminal.
This convention can be a source of confusion, particularly when dealing with more complex circuits or with circuits that involve alternating current (AC) rather than direct current (DC). However, it is important to be aware of the convention and to use it consistently when analyzing and designing circuits.
In different current-carrying materials, the charges of the moving particles may be positive or negative. In metals, the moving charges are always (negative) electrons, while in an ionized gas (plasma) or an ionic solution, the moving charges may include both electrons and positively charged ions. In a semiconductor material such as germanium or silicon, conduction is partly by electrons and partly by motion of vacancies, also known as holes; these are sites of missing electrons and act like positive charges.
