Transcription of Temperature coefficient of resistivity
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Temperature coefficient of resistivity
Temperature coefficient of resistivity )]TT(1[oo + = )]TT(1[RRoo += T0 = reference Temperature = Temperature coefficient of resistivity , units of( C)-1 For Ag, Cu, Au, Al, W, Fe, Pt, Pb: values of are ~3-5 10-3 ( C)-1 Tslope = )]TT(1[RRoo +=Example: A platinum resistance thermometer uses thechange in R to measure Temperature . Suppose R0 = 50 at T0=20 C. for Pt is 10-3 ( C)-1 in this Temperature is R when T = C?R = 50 [1 + 10-3 ( C)-1 ( C)] = Temperature coefficient of resistivityExample: A platinum resistance thermometer has aresistance R0 = at T0=20 C. for Pt is 10-3( C)-1. The thermometer is immersed in a vesselcontaining melting tin, at which point R increases . What is the melting point of tin?)]TT(1[RRoo += = 50 [1 + 10-3 ( C)-1 (T 20 C)] = [1 + 10-3 ( C)-1 (T 20 C)] = 10-3 ( C)-1 (T 20 C)212 C = T 20 CT = 232 CLight bulbsInert gas (typically Ar) is used to make sure that filamentis housed in an O-free environment to preventcombustion reaction between W and Sir Joseph Swan (1878) &American Thomas Edison (1879).
electromagnets, to be discussed in future chapters. Example: Consider a microwave oven, a toaster, and a space heater, all operating at 120 V: Toaster: 1000 W Microwave: 800 W Heater: 1300 W How much current does each draw? I = P/ΔV Toaster: I = 1000W/120V = 8.33A Micro: I = 800W/120V = 6.67A
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