Resistors

            As the name suggests, these elements resist the flow of electric current.

Resistance in series and parallel

Resistors in series add together as R1 + R2 + R3 + ….. While resistors in parallel reduce by 1 / (1 / R1 + 1 / R2 + 1 / R3 + …..).

Resistance and Power

It follows as a fundamental rule in using resistors in electronic circuits that the resistor must be able to comfortably handle the power it will dissipate. A rule of thumb is to use a wattage rating of at least twice the expected dissipation. (P = I * I * R)

Common resistors in use in electronics today come in power ratings of 0.25W, 0.5W, 1W and 5W. Other special types are available to order. Because of precision manufacturing processes it is possible to obtain resistors in the lower wattage ratings which are quite close in tolerance of their designated values. Typical of this type are the .25W range which exhibit a tolerance of plus / minus 2% of the value.

Resistance color chart codes

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