Fundamental Electrical and Electronic Principles, Third Edition

semiconductorFundamentals 23R (Ω)conductor0 θ (°C)measurement is per degree, e.g. /°C. The reference temperature usuallyquoted is 0°C, and the resistance at this temperature is referred to asR 0 . Thus the resistance at some other temperature u 1 °C can be obtainedfrom:R RFig. 1.13( 1αθ ) ohm (1.14)1 0 1In general, if a material having a resistance R 0 at 0°C has a resistanceR 1 at θ 1 C and R 2 at θ 2 C, and if α is the temperature coefficient at0°C, thenR R ( 1αθ) and R R ( 1αθ)1 0 1 2 0 2so R R121 αθ1αθ12(1.15)Worked Example 1.18Q The field coil of an electric motor has a resistance of 250 Ω at 15°C. Calculate the resistance if themotor attains a temperature of 45°C when running. Assume that α 0.00428/°C referred to 0°C.AUsing equation (1.15):R 1 250 Ω ; u 1 15°C; u 2 45°C; α 4.28 10 3250 1 4 28 035 ( . 1 1 )R 1( 428 . 10345)2250 0.8923R2R 280. 2Ω Ans2