2.02 Electrical current (i)

Electrical current is a measure of the rate of flow of electrical charge through a material. Consider an electrical current flowing through a wire. The magnitude of the electrical current will depend on

  I = naqv


 I   =   naqv   =    2x1028m  x   2.5x10-6  x   1.6 x 10-19  x   1x 10-3    =   8 Amps

Note the symbol q represents the amount of charge carried by the mobile charge carriers within the material. If the material is a liquid or gas the charge carriers could be positive or negative ions as well as electrons. The charge on ions can vary depending on the level of ionisation. In solid materials the only charge carriers which are free to move are electrons. The charge on an electron is fixed (1.6 x 10-19 C). Because we are often dealing with solid conductors the symbol q is sometimes replaced by the symbol e to represent the charge on the electron.

  I = nave

As well as replacing q by e, the right hand side of the equation has been rearranged to make it easier to remember. As the values on the right hand side of the equation are multiplied together it does not matter which way round we write them