Identifying Carbon Resistors

Resistors are used in electrical circuits to control the flow of current.

If you look at resistors, you will see most are small cylinders about six millimeters long and three millimeters wide with coloured bands around the body (not power resistors, these are not covered in this section).

The coloured bands on resistors are used to tell the resistance value as they conform to a standard colour code which can express any number close to its value by rounding it off to the first two digits in the number.

For example 57,224 can be rounded to 57,000 and still be within one percent of its value, using two digits and the required number of zeros can express any number close enough to the actual value.

The coloured bands in Fig 11 illustrate the allocation of a number from 0 to 9.

• Bands one and two, reading from the left are the two digits of the resistors value
• Band three indicates how many zeros follow the two numbers
• Band four, not always present indicates
  resistor tolerance.
  • Red = 2%,
  • Gold = 5%
  • Silver = 10%

Fig 11