In the RHS of the page is a nomograph for calculating electrical quantities, OHM’S LAW. This powerful, simple group of interrelated formulas is the foundation of all electrical and electronic engineering and hence the modern technological age. The nomograph is divided into four quadrants, each defining an electrical term; W = Power in WATT’S; I = Current flow in AMPERE’S; R = Resistance in OHM’S; E =
Electromotive force in VOLT’S.
It is a fact that when one wishes to calculate the value of one of these terms, two of the others will invariably be known. It is thus a simple matter to select and apply one of the three formulas in the outer ring of that quadrant. For example, suppose we wish to calculate the resistance of a 12 volt 20 watt light bulb, we refer to the quadrant marked R and note that this can be solved by squaring the voltage and then dividing by the wattage, so, 12 times 12 divided by 20 = 7.2 ohms.