Watts ÷ 746 = the number of horse-power.
(See Transformers, also Elementary Electrical Examples.)
356. Ohm's Law. It was first shown by Ohm that the strength of a current is equal to its E. M. F. divided by the resistance in the circuit; that is,
Strength of current (amperes) = E. M. F. (volts). / resistance (ohms).
If we let C stand for the strength in amperes, E for the E. M. F. in volts, and R for the resistance in ohms, we have the short formula, easily remembered,
C = E/R
357. An Ampere would be produced by a current of 1 volt pushing its way through a resistance of 1 ohm. Knowing any two of the three, C, E, or, R, the other may be found. The resistance, R, it must be remembered, is the total resistance in the circuit, and is composed of the total internal and external resistances.
(See Elementary Electrical Examples.)
358. Internal Resistance and Current Strength. It is evident that the internal resistance of a cell varies with the position and size of the plates. We shall now study the effects of these changes upon the strength of the current.