The heat developed by a current in a circuit is proportional (a) to the square of the current, (b) to the resistance of the circuit1, (c) to the time during which the current passes. Hence,
in which I represent the current in amperes, R the resistance in ohms, t the time in seconds, and m a constant factor 'depending on the kind of heat units in which it is desired to express H. If H is to be calories,
This heating effect is a waste in many uses of the current, such as in the conducting wires of a street railway, or of a system of electric lighting. It is called the heat los8 and reduces the efficiency of the
system. It is made use of, however, in electric heating, such as the heating of cars, in which the current passes through coils of resistance wire, and in cooking utensils, water heaters, toasters, flatirons, soldering irons, etc.
Fig 1.-Base of Electric Heater, partly cut away
