Resistance Laws

Author: J.B. Hoag

The same opposition to the flow of water through a series of pipes of large and small diameter can be attained by a single pipe of proper size. So also, a single resistance can be found in electrical circuits which is the equivalent of a combination of several resistances in series with each other. Instead of connecting the pipes or the resistances in series with each other, they might be joined in parallel, or in more complex series and parallel combinations. In all cases, however, they can be replaced by a single, equivalent unit. The laws for a number of typical circuits are given in Figs. 2 A through 2 E.

Fig. 2 A. For resistances in series

Fig. 2 B. For resistances in parallel

Fig. 2 C. For no current flow from A to B

Fig. 2 D. For shunts, the current i is given by the equation above

Fig. 2 E. For voltage dividers

Fig. 2 F. A decibel chart (click on the image to get a closer view)