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www.GOALias.blogspot.comResistors in the higher range are made mostly from carbon. Carbonresistors are compact, inexpensive and thus find extensive use in electroniccircuits. Carbon resistors are small in size and hence their values aregiven using a colour code.CurrentElectricityTABLE 3.2 RESISTOR COLOUR CODESColour Number Multiplier Tolerance (%)Black 0 1Brown 1 10 1Red 2 10 2Orange 3 10 3Yellow 4 10 4Green 5 10 5Blue 6 10 6Violet 7 10 7Gray 8 10 8White 9 10 9Gold 10 –1 5Silver 10 –2 10No colour 20The resistors have a set of co-axial coloured ringson them whose significance are listed in Table 3.2. Thefirst two bands from the end indicate the first twosignificant figures of the resistance in ohms. The thirdband indicates the decimal multiplier (as listed in Table3.2). The last band stands for tolerance or possiblevariation in percentage about the indicated values.Sometimes, this last band is absent and that indicatesa tolerance of 20% (Fig. 3.8). For example, if the fourcolours are orange, blue, yellow and gold, the resistancevalue is 36 × 10 4 Ω, with a tolerence value of 5%.3.8 TEMPERATURE DEPENDENCE OFRESISTIVITYThe resistivity of a material is found to be dependent onthe temperature. Different materials do not exhibit thesame dependence on temperatures. Over a limited rangeof temperatures, that is not too large, the resistivity of ametallic conductor is approximately given by,ρ T= ρ 0[1 + α (T–T 0)] (3.26)where ρ Tis the resistivity at a temperature T and ρ 0is the same at areference temperature T 0. α is called the temperature co-efficient ofresistivity, and from Eq. (3.26), the dimension of α is (Temperature) –1 .FIGURE 3.8 Colour coded resistors(a) (22 × 10 2 Ω) ± 10%,(b) (47 × 10 Ω) ± 5%.103