Museo Galileo
Virtual Museum
Voltage (tension)

To explain voltage in simple terms, we can use a hydraulic analogy. A current will flow through a tube connecting two vessels only when the liquid is at a different level in each vessel. A wire connecting two electrically charged bodies will carry an electric current only if the bodies have different voltages. The difference in the height of the liquid in the vessels is comparable to the potential difference (formerly tension, now voltage) between the electrified bodies.