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Resistors

Resistors are the most commonly used component in electronics and their purpose is to create specified values of  current and voltage in a circuit. A number of different resistors are shown in the photos. (The resistors are on millimeter paper, with 1cm spacing to give some idea of the dimensions). The left photo shows some low-power resistors, while the right shows some higher-power resistors. Resistors with power dissipation below 5 watt (most commonly used types) are cylindrical in shape, with a wire protruding from each end for connecting to a circuit. Resistors with power dissipation above 5 watt are shown below .

Some low-power resistors High-power resistors and rheostats

The symbol for a resistor is shown in the following diagram (left: American symbol, right: European symbol.)

Resistor symbols

The unit for measuring resistance is the OHM. (the Greek letter Ω). Higher resistance values are represented by "k" (kilo-ohms) and M (meg ohms). For example, 120 000 Ω is represented as 120k, while 1 200 000 Ω is represented as 1M2. The dot is generally omitted as it can easily be lost in the printing process. In some circuit diagrams, a value such as 8 or 120 represents a resistance in ohms. Another common practice is to use the letter E for resistance. For example, 120E (120R) stands for 120 Ω, 1E2 stands for 1R2 etc.

Resistor Color Code

 

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