How can you tell the resistance of a composition resistor?

• A. A series of colored bands.
• B. A digital readout.
• C. A printed value on the body.
• D. A temperature rating.

Answer: (A)

Color bands on a carbon composition resistor encode its resistance value. In the common four-band color code, the first two bands are the significant digits, the third band is the multiplier (a power of ten), and the fourth band shows tolerance. The color-to-number mapping is standard: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, gray 8, white 9. By reading the first two bands as digits, applying the multiplier from the third, and noting the tolerance from the fourth, you determine the resistance. For example, red, violet, yellow, gold translates to 27 with a multiplier of 10^4, giving 270,000 ohms (270 kΩ) with about ±5% tolerance. Printed values or digital readouts aren’t the typical way to read a carbon composition resistor, and the temperature rating isn’t how you determine its resistance.