The heater element of a 120-V toaster is a 5.1-m length of nichrome wire, whose
ID: 1982216 • Letter: T
Question
The heater element of a 120-V toaster is a 5.1-m length of nichrome wire, whose diameter is 0.63 mm. The resistivity of nichrome at the operating temperature of the toaster is 1.3 x 10-6 . The nichrome wire is replaced by a 5.5-m length of tungsten wire. The power of the toaster, when operated at a voltage of 120 V, remains unchanged when the wire replacement is made. The resistivity of tungsten, at the operating temperature of the toaster, is 2.4 x 10-7 . The diameter of the tungsten wire is closest to:0.12 mm
0.17mm
0.32mm
0.22mm
0.27mm
Explanation / Answer
By R = rho x L/A =>R = [1.3 x 10^-6 x 5.1]/[pi x r^2] =>R = [1.3 x 10^-6 x 5.1]/[3.14 x (0.25 x 10^-3)^2] =>R = =>By P = V^2/R =>P = 120 x 120/R answer is 0.27 mm
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