A resistor is a two-terminal electronic component that opposes an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V = IR. The electrical resistance R is equal to the voltage drop V across the resistor divided by the current I through the resistor. Resistors are used as part of electrical networks and electronic circuits.
Identifying resistors
Most axial resistors use a pattern of colored stripes to indicate resistance. Surface-mount resistors are marked numerically. Cases are usually tan, brown, blue, or green, though other colors are occasionally found such as dark red or dark grey.
One can also use a multimeter or ohmmeter to test the values of a resistor
Four-band axial resistors
Main article: Electronic color code
Four-band identification is the most commonly used color coding scheme on all resistors. It consists of four colored bands that are painted around the body of the resistor. The first two numbers are the first two significant digits of the resistance value, the third is a multiplier, and the fourth is the tolerance of the value.
For example, green-blue-yellow-red is 56 x (10^4) Ω = 560 kΩ ± 2%).
Each color corresponds to a certain number, shown in the chart below. The tolerance for a 4-band resistor will be 1%, 5%, or 10%.
Color 1st band 2nd band 3rd band(multiplier) 4th band(tolerance)
Black 0 0 × 100
Brown 1 1 × 101 ±1%
Red 2 2 × 102 ±2%
Orange 3 3 × 103
Yellow 4 4 × 104
Green 5 5 × 105 ±0.5%
Blue 6 6 × 106 ±0.25%
Violet 7 7 × 107 ±0.1%
Gray 8 8 × 108 ±0.05%
White 9 9 × 109
Gold × 10-1 ±5%
Silver × 10-2 ±10%
None ±20%
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