Demonstration of the change in conductivity of a solution when a strong acid is added. In the solution are two wires, connected to a circuit containing a battery and a light bulb. If a current flows, the light bulb will light up, which in this case it does. Strong acids are those dissociate almost completely in solution, producing a large number of free ions. A current is the movement of charged ions, and the presence of ions here is seen by the flowing current and lit bulb. For the same experiment with a weak acid, see clip K004 3149.