Conventional Current

In a real circuit, the particles that actually move are electrons, flowing from the negative terminal of the battery, through the external circuit, and back into the positive terminal. However, by a convention that was fixed by scientists (including Benjamin Franklin) long before the electron was even discovered, the arrows drawn in every circuit diagram to indicate the direction of current always point from the positive terminal of the battery, through the external circuit, to the negative terminal -- the direction in which a positive test charge would move if it were free to do so.

This universally used direction is called the conventional current, or simply "current". Because the charges that are actually flowing in a typical metallic circuit are negative electrons, the true direction of electron flow is exactly opposite to the direction of conventional current: as electrons stream from the negative terminal to the positive terminal, the arrows on the diagram show current flowing from positive to negative. This is not a contradiction, because a transfer of positive charge in one direction is, in every physical respect that matters for a circuit's behaviour, mathematically equivalent to a transfer of the same amount of negative charge in the opposite direction; both descriptions predict identical forces, identical heating effects and identical circuit behaviour, so physicists simply kept the older, pre-electron convention rather than reversing every circuit diagram ever drawn. It …