There is a definite relation between the volts, ohms, and amperes of a circuit of electricity. This relation was first stated by a man named Ohm, and is known as Ohm's Law.
The quantity of electricity in amperes delivered by a circuit is obtained by dividing the electromotive force in volts by the resistance in ohms. This rule may be abbreviated into a formula:
Amperes = Volts / Resistance
I = E / R where I is the quantity of electricity in amperes, E the electromotive force in volts, and R the resistance in ohms. By transformation of the formula
E = RI
R = E / I
Thus, if we know any two of the three units of a circuit, it is possible to find the third.