## Conventional Electric Current

Electric current &nbsp;

$I$
&nbsp; is defined as the charge &nbsp;Q

&nbsp;in Coulombs passing a point per unit time &nbsp;
$t$
&nbsp; or &nbsp;
$I=\frac{Q}{t}$
.
Wherever electric charges move an electric current is created. Usually only electrons carry electric charge. This is the case for all solids. Positively charged atoms are foxed in positions and only electrons are able to move. In a gas or solid, atoms may sometimes become ionised or charged - usually positive - and are then able to carry charge and current.
The single characteristic that separates metals from other materials is the presence of free electrons. Free electrons are able to move throughout the materials and so they are free to carry electric charge - being negatively charged - and electric current. Electrons, being negative, are repelled by negative charges and attracted by positive charges. Because of a historical accident, we consider the flow of electric current as being from positive to negative and call it the 'conventional current' - and the electric field as being in the direction of the force on a positive charge.