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Resistors shape the most fundamental and significant constituent among the group of lumped circuit elements. Resistors are the most ordinarily utilized segment as a part of hardware and their motivation is to make determined estimations of current and voltage in a circuit. A resistor can be characterized as a passive two-terminal electrical component that offers electrical resistance as a circuit component. Being a passive element, resistors convey the prime usefulness of offering resistance/impedance to the way of free current stream. Resistors act to restrict current flow, and, in turn also lower the voltage level in circuits. In electronic circuits, resistors are utilized to limit current flow, adjust signal levels, bias active elements, and terminate transmission lines among various other usages. High-power resistors, that can dissipate numerous watts of electrical power as thermal energy, may be utilized as a major aspect of engine controls, in power distribution frameworks, or as test loads for generators. Fixed resistors have resistances which would depend somewhat upon temperature, time or external voltage. Variable resistors can be utilized to modify circuit components, (for example, a volume control or a light dimmer), or as detecting gadgets for warmth, light, humidity, power, or chemical activity.

Resistors are regular components of electrical systems and electronic circuits and are pervasive in electronic hardware. Practical resistors as discrete parts can be composed of different compounds and structures (metal film, carbon film, wire-wound resistors). Resistors are obtained as components in integrated circuits.

The electrical function of a resistor is specified by its resistance, symbol is Ω(ohms): common commercial resistors are manufactured over a range of more than nine orders of magnitude. The nominal value of the resistance will fall within a manufacturing tolerance.

Various distinctive resistors are appeared in the photographs. Fig. 1(a) demonstrates some low-power resistors, while Fig. 1(b) demonstrates some higher-power resistors. Resistors with power dissipation below 5watts (most generally utilized types) are cylindrical in shape, with a wire projecting from every end for connecting with a circuit (Fig. 1(a)). Resistors with power dissipation of above 5watt are shown as under (Fig. 1(b)).

Fig. 1: (a) Low-power resistors and (b) High-power resistors.

Resistors_1The basic schematic for a resistor is represented as follows (Fig. 2 upper: American image, lower: European image.)

Fig. 2: Resistor symbols.


Higher resistance qualities are spoken to by “k” (kilo-ohms) and “M” (meg ohms). For instance, 12×103Ω is represented as 12kΩ, while 12×106Ω is represented as 12MΩ. Resistors regularly accessible in commercial market are available as multiples of 12 particular values known as Referred values denoted by E12 or R12. The numbers are: – 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68 and 82 respectively. Resistor values lying intermediate to those predefined as above can be acquired by connecting the resistors in series or parallel combination to produce the required equivalent resistance. Fig. 3 demonstrates a combination of resistors in series and parallel configuration. The three resistors in arrangement (in Fig. 3(a)) would bring about an equivalent resistance of 3R whereas, the circuit graph in Fig. 3(b) would bring about an equivalent resistance of 3R/2 (i.e., 1/R + 1/R = 2/R, hence reciprocal would be R/2. Therefore, R/2 + R = 3R/2 is the overall equivalent resistance).

Fig. 3: (a) Resistors in series, (b) Resistors in parallel and series configuration.