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Electric current

A piece of wire is made of millions of atoms and each one of these has its own cloud of electrons. However in a metal there is a large number of electrons that are not held around particular nuclei but are free to move at high speed and in a random way through the metal. These are known are free electrons and in a metal there are always large numbers of these. An electric current is a movement of these free electrons in a certain direction by the application of a voltage.

Each electron has only a very small amount of electric charge, and it is more convenient to use a larger unit when measuring practical units of charge. This unit is the coulomb.

The charge on one electron is -1.6x10-19 C. Usually written as e.

The Amp can be defined in the following way:

A current of 1A flows in a wire if a charge of 1C passes any point in the wire each second.

Current = Charge / Time or Charge = Current x Time
© Keith Gibbs 2011