Fig. 74
This warms the plate slightly—enough to keep food warm which has been already cooked. This costs about one cent an hour.
When the switch is placed upon the second point the current goes through 56 ohms of resistance and 2 amperes pass.
(112 volts)/(56 ohms) = 2 amperes.
This makes the plate warmer and is adapted to certain cooking processes. It costs about two cents an hour.
When the switch is placed upon the third point the current goes through 28 ohms of resistance and 4 amperes pass.
(112 volts)/(28 ohms) = 4 amperes.
We placed upon this hot plate a basin containing 1 pint of water (equals 1 pound) and heated it from the temperature of the room (68 degrees) to boiling (212 degrees) in 7 minutes and then put an egg in and boiled it 3 minutes. Using 4 amperes for 10 minutes cost two thirds of a cent. If it takes 7 minutes to boil a pint of water it would require 1 hour to boil a gallon upon this hot plate using 4 amperes, or 448 watts. That is, it costs us about 4.5 cents a gallon to boil water by electricity. The cost is usually put at three and a half cents per gallon, but much depends upon conditions.