Question

Two wires have the same cross-sectional area and are joined end to end to form a single wire. The first wire has a temperature coefficient of resistivity of α1 =0.00480 (C°)-1 and a resistivity of 4.90 x 10-5Ω m. For the second, the temperature coefficient is α2 = -0.000600 (C°) -1 and the resistivity is 4.60 x 10-5Ω m, respectively. The total resistance of the composite wire is the sum of the resistances of the pieces. The total resistance of the composite does not change with temperature. What is the ratio of the length of the first section to the length of the second section? Ignore any changes in length due to thermal expansion.

Answer 1

resistanc=resitivity*length/Area * coeffThermal*deltaTemp


setting resistance the same

resisitive1*length1/area1*coeff1*dettaT1=resistivity1*length2/area2*cxoeff2*deltatT2

areas, deltatemps are same, so in my head..

length1/length2=coeff2/coeff1 * resisitive2/resisitivity1

check my thinking.