Resistance is a property that describes how a material or component resists the flow of electrical current. It is the ratio of voltage (V) applied across a component to the current (I) passing through it and is expressed as R = V/I.
The color bands on a resistor are used to represent the resistance value, tolerance, and sometimes the temperature coefficient of the resistor. These color bands follow a standardized color code to help identify the resistor's characteristics. The number of color bands on a resistor can vary, but most commonly, you will find resistors with either four or five bands.
Significant Figure Bands (1st and 2nd Bands): These bands represent the significant digits of the resistance value. Each color corresponds to a specific number, typically from 0 to 9. The first band represents the tens digit, and the second band represents the units digit.
| Color | Value |
|---|
| Black | 0 |
| Brown | 1 |
| Red | 2 |
| Orange | 3 |
| Yellow | 4 |
| Green | 5 |
| Blue | 6 |
| Violet | 7 |
| Gray | 8 |
Multiplier Band (3rd Band): This band represents the multiplier that should be applied to the significant figures to get the full resistance value. Each color corresponds to a power of 10.
| Color | Value |
|---|
| Black | x1 |
| Brown | x10 |
| Red | x100 |
| Orange | x1,000 |
| Yellow | x10,000 |
| Green | x100,000 |
| Blue | x1,000,000 |
| Violet | x10,000,000 |
| Gray | (rarely used for multipliers) |
| White | (rarely used for multipliers) |
Tolerance Band (4th Band, if present): The tolerance band indicates the allowable percentage deviation from the nominal resistance value. The most common tolerance values are:
| Color | Value |
|---|
| Gold | ±5% |
| Silver | ±10% |
| No color (bare) | ±20% |
Temperature Coefficient Band (5th Band, if present): Some resistors, especially precision resistors, include a fifth band to indicate the temperature coefficient. The temperature coefficient band tells you how much the resistor's resistance changes with temperature.
| Color | Value |
|---|
| Brown | ±100 ppm/°C (parts per million per degree Celsius) |
| Red | ±50 ppm/°C |
| Orange | ±15 ppm/°C |
| Yellow | ±25 ppm/°C |
| Blue | ±10 ppm/°C |
Sixth Band (Temperature Coefficient or Reliability): The sixth band, if present, provides information about the temperature coefficient or, in some cases, the reliability or failure rate of the resistor.
| Color | Value |
|---|
| Brown | ±100 ppm/°C (parts per million per degree Celsius) |
| Red | ±50 ppm/°C |
| Orange | ±15 ppm/°C |
| Yellow | ±25 ppm/°C |
| Blue | ±10 ppm/°C |
Factors Affecting Resistance:
- Material: Different materials have different electrical resistivity, which influence their resistance. For example, metals like copper have low resistivity, making them good conductors, while insulators have high resistivity.
- Length: The longer a wire or component, the more resistance it typically has.
- Cross-Sectional Area: A wider cross-sectional area generally results in less resistance.
- Temperature: Resistance can change with temperature. Some materials, like conductors, generally have increasing resistance with temperature, while semiconductors may decrease in resistance with higher temperatures.
