3 Resistivity of Various Materials
Resistivity of Various Materials
- Metals have low resistivities. It is in the range of 10−8 Ω m to 10−6 Ω m. Insulators have resistivities 1018 times greater than metals. Semi-conductors lie in between them.
Resistors are of two types:
(i) Wire bound resistor
(ii) Carbon resistor
- Carbon resistors are very small in size. Therefore, their values are given using a colour code.
| TABLE 3.2 RESISTOR COLOUR CODES | |||
| Colour | Number | Multiplier | Tolerance (%) |
| Black | 0 | 1 | |
| Brown | 1 | 101 | |
| Red | 2 | 102 | |
| Orange | 3 | 103 | |
| Yellow | 4 | 104 | |
| Green | 5 | 105 | |
| Blue | 6 | 106 | |
| Violet | 7 | 107 | |
| Gray | 8 | 108 | |
| White | 9 | 109 | |
| Gold | 10−1 | 5 | |
| Silver | 10−2 | 10 | |
| No colour | 20 | ||
- Here, first two bands from one end indicate the first two significant figures of resistance in ohms.
- Third band indicates the decimal multiplier.
- The last band stands for tolerance. Its absence indicates a tolerance of 20%.