by Barnaby Meins

Created on: May 21, 2008

The electron carries a negative elementary or unit charge while the proton carries a positive charge in an atoms, the basic unit of matter. The two types of charge are equal and opposite. The unit of electrical charge in the International System of Units is the coulomb (symbolized C), where 1 C is equal to approximately 6.24 x 10 to the power of 18 elementary charges. Charge, also known as electric charge or electrostatic charge and symbolized q, is a characteristic of a unit of matter that expresses the extent to which it has more or fewer electrons than protons.

Current is a flow of electrical charge carriers, usually electrons or electron-deficient atoms. The common symbol for current is the uppercase letter I. The standard unit is the ampere, symbolized by A. One ampere of current represents one coulomb of electrical charge moving past a specific point in one second.

An electric field is the effect produced by the existence of an electric charge, such as an electron, ion, or proton, in the volume of space or medium that surrounds it. The electrical potential energy at a given point is defined to be the negative of the work an external force would have to do to move a charge from the location chosen as the zero reference level to the point.

Voltage is a quantitative expression of the potential difference between two points in an electrical field. The greater the voltage, the greater the flow of electrical current, that is, the quantity of charge carriers that pass a fixed point per unit of time through a conducting or semi-conducting medium for a given resistance to the flow. Voltage is symbolized by an uppercase italic letter V or E. The standard unit is the volt, symbolized by a non-italic uppercase letter V.

Two basic laws by Kirchoff, which are Kirchhoff's current law and Kirchhoff's voltage law are used in applied electronics for determining the current and voltage in an electrical circuit.
Kirchhoff's current law states that the total currents flowing into or out of any node is zero. This rule is a consequence of the fact that the flow of charge is conserved in steady-state flow. There would be a build up of charge at any circuit junction if less charge flowed out of the junction than flowed into the junction.

Kirchhoff's voltage law states that the sum of voltage drops around a loop is zero. The superposition theorem mentions that the total current in any part of a linear circuit equals the algebraic sum of the currents produced by each source separately.

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