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FIG. 11. Hydraulic Analogy between Voltage and Amperage.

The accompanying sketches show graphically the analogy between the voltage and amperage of an electric current and the pressure and volume of a stream of water. In the first illustration a tank is shown at a high elevation from which a small pipe leads. The voltage or pressure in such a pipe would be high in comparison with that in a pipe leading from a lower tank.

In the second illustration the pipe leading from the tank is much larger than that from the first and consequently the amperage or volume flowing is greater in comparison. From this it may be readily seen that every circuit through which a current is flowing must exhibit both quantities.

The unit of electrical work or energy is the Watt. Seven hundred and forty-six watts constitute an electrical horse-power. The number of watts is indicated by the voltage times the amperage. Thus the amount of energy in a circuit in which 50 amperes at 100 volts pressure are passing is 50 x 100 or 5,000 watts.