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MANAGERS AND PROJECTIONISTS 53
the vehicle through which pressure or E. M. F. works, and that in the production of power in any form it is voltage (pressure) and not amperage (volume) which is consumed.
In a steam engine, with the steam at given pressure we may increase the power of the engine by either increasing the area of the piston or the length of its strokes or by increasing the pressure of the steam. In a water motor we may increase the capacity to do work either by increasing the size of the motor or the pressure of the water. The same thing holds true with electricity. We may increase its capacity to do work either by increasing the volume of current (amperage) or by increasing the voltage. To perform a given amount of work with a low pressure (voltage) a large volume (amperage) is necessary, but if the voltage be high the same amount of work can be performed with much less volume of current. The horse power of work performed by electric current is represented by the voltage times the amperes divided by 746.H.P. = Volts x Amperes -* 746.
OHM. — In passing through a pipe water encounters resistance by reason of the rough sides of the pipe, as well as by reason of the internal resistance of the water itself. This resistance tends to retard the flow. Precisely the same is true with electricity. In passing through a wire electric current encounters resistance, and this resistance tends to retard the flow of current. It is measured in ohms, the definition of which is given on page 35.
The effect of resistance is to produce heat. In other words power consumed in overcoming resistance is transformed into heat. In a water pipe the resistance increases as the volume of water passing through a pipe of given diameter is increased, or as the diameter of the pipe is made smaller with relation to the volume of water flowing. The same thing is true of current. Having a wire of given diameter its resistance increases as the current flow becomes greater, and decreases as the current flow becomes less, or, having a given current flow, the resistance decreases as the diameter of the wire is made greater, or its length is decreased.
WATT.— Watt is the unit used to measure the amount of electrical energy expended — the amount of work actually performed. It is found by mutiplying the voltage by the number of amperes, and is transformed into horsepower by dividing that result by 746, since 746 watts is equal to one electrical horsepower. For example: If we have 10 amperes at 110 volts the amount of energy expended would be equal to 110 x