Joules’ law may be stated as follows:
The heat generated in a conductor by an electric current is proportional to the resistance of the conductor, the time during which the current flows, and the square of the strength of the current.
The quantity of heat in calories may be calculated by use of the equation,
calories per second = volts × amperes × .24. (1)
The total number of calories H developed in t seconds will be given by
H = P.D. × C × t × .24. (2)
EXAMPLE—If a current of 10 amperes flows in a wire whose terminals are at a potential difference of 12 volts, how much heat will be developed in 5 minutes?
Substituting in equation (2):
10 × 12 × (60 × 5) × .24 = 8640 calories.
Since by Ohm’s Law potential difference = I × R substituting IR for P.D. in (2)