Colour Code for Resistors
The colour code system is used to indicate the resistance value on carbon resistors using coloured bands. Usually, 4-band resistors are used. The bands represent:
- 1st band: First significant digit
- 2nd band: Second significant digit
- 3rd band: Multiplier (power of 10)
- 4th band: Tolerance
Colour Code Table
| Colour | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | \( \times 10^0 \) | – |
| Brown | 1 | \( \times 10^1 \) | ±1% |
| Red | 2 | \( \times 10^2 \) | ±2% |
| Orange | 3 | \( \times 10^3 \) | – |
| Yellow | 4 | \( \times 10^4 \) | – |
| Green | 5 | \( \times 10^5 \) | ±0.5% |
| Blue | 6 | \( \times 10^6 \) | ±0.25% |
| Violet | 7 | \( \times 10^7 \) | ±0.1% |
| Gray | 8 | \( \times 10^8 \) | ±0.05% |
| White | 9 | \( \times 10^9 \) | – |
| Gold | – | \( \times 10^{-1} \) | ±5% |
| Silver | – | \( \times 10^{-2} \) | ±10% |
| None | – | – | ±20% |
Formula:
\[ \text{Resistance} = (AB) \times 10^C \quad \text{with tolerance } \pm D\% \]
Example 1:
Red – Violet – Yellow – Gold
Digits: Red = 2, Violet = 7, Yellow = \( \times 10^4 \), Tolerance = ±5%
\[ R = (27) \times 10^4 = 270000 \, \Omega = 270 \, k\Omega \pm 5\% \]
Example 2:
Brown – Black – Red – Silver
Digits: Brown = 1, Black = 0, Red = \( \times 10^2 \), Tolerance = ±10%
\[ R = (10) \times 10^2 = 1000 \, \Omega = 1 \, k\Omega \pm 10\% \]
This is how the colour bands are used to read resistance values and tolerances for carbon resistors.
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