Introduction. Resistors are electronic components that restrict the flow of current
Resistors are electronic components that restrict the flow of current. Figure 1. shows the different resistor symbols that are used in circuit diagrams. The first a rectangular box is used throughout Europe, while the zig-zag line is more common in Japan and the USA.
Figure 1. Resistor symbols in common use.
The unit of resistance is [V.A-1], which is given the name, the Ohm. [Ω] in honour of the physicist and mathematician, Georg Simon Ohm (1787-1854). Ohm is most famous for the law that bares his name Ohm’s law
Inside a Resistor
Resistors are made in several different ways, and although they just look like blobs on a wire, they are quite interesting.
Resistor Networks
Amlost any non-trival electrical circuit will contain some resistors in series and parallel, therefore it is necessary to be able to work out the equivalent resistances of the network.
Series
Resistors in series have the same current flowing across them but different voltages. The total potential drop across the resistors in series is V=V1 + V2.
Using Ohm’s law
V=IReq = IR1 + IR2.
Req=R1 + R2.
The resistance of N different resistors in series is the sum of each resistor. In a series configuration, the current through all of the resistors is the same, but the voltage across each resistor will be in proportion to its resistance. The potential difference (voltage) seen across the network is the sum of those voltages, thus the total resistance can be found as the sum of those resistances:
As a special case, the resistance of N resistors connected in series, each of the same resistance R, is given by NR.