24.002 Flow of electrons

Jackie Adams and Robert Hutchings
Electronics, 1997
Pages 3-4, Flow of electronics

Before you start to build your own electronic circuits, you need to have an understanding of basic electrical theory.

1.2 Basic Concepts

Electronics is largely concerned with the controlled movement or flow of electrons, and such movement occurs most easily in metallic materials which are said to have a low resistance (or high conductivity) and are classified as conductors. Materials which offer an extremely large opposition to electron flow are known as insulators.

When a potential (or voltage) difference, supplied by a battery for example, is applied across a conductor, it causes a current to pass through it. The electric current is a measure of the rate of flow of electrons (negatively charged particles) past any point in the circuit. The charge Q which flows past a point in time t if there is a constant current I, is given by the equation

charge, Q = current,I x time,t Q = It

The unit of charge is the coulomb. One coulomb (1 C) is the charge that in one second (1 s) crosses a section of a circuit in which there is a current of one ampere (1 A).

The potential difference (p.d.) between two points in a circuit is defined as the electrical energy converted to other forms of energy when unit charge passes from one point to the other, i.e. the electrons dissipate energy as they pass through a resistive circuit. The unit of potential difference is the volt. One volt (1 V) is the potential difference between two points in a circuit when one joule of energy is converted when one coulomb passes from one point to the other.

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