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(--) cli. Secure I https/ netyweb/Student/Assignment-Responses/astdep-17194115 High-voltage power lines are a familiar sight throughout the country. The aluminum wire used for some of these lines has a cross-sectional area of 4.80 × 10 4 m, what is the resistance of ten kilometers of this wire? Additional Materials Section 20.3 7. -11 points CJ10 20.P018 My Notes O Ask Your Tead A tungsten wire has a radius of 0.083 mm and is heated from 20.0 to 1220 °C. The temperature coefficient of resistivity is 4.5 x 10-3 (C")-1 when 220 V is applied across the ends of the hot wire, a current of 1.4 A is produced. How long is the wire? Neglect any effects due to thermal expansion of the wire. Additional Materials DOLLExplanation / Answer
length of the wire L = 10 km = 10000 m
cross sectional area A = 4.8*10^-4 m^2
resistivity of aluminiumrho = 2.65*10^-8 ohm m
resistance R = rho*L/A
R = 2.65*10^-8*10000/(4.8*10^-4) = 0.552 ohm
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potential applied v = 220
current I = 1.4
resistance Rt = V/I = 220/1.4 =157.1 ohm
resitivity of tungsten rho at 20 degrees = 5.6*10^-8 ohm m
resitivity of tungsten rho at 1220 degrees = rho(1 + (alpha*dT) )= (5.6*10^-8)( 1 + (4.5*10^-3*(1220-20))) = 3.584*10^-7
resistance Rt = rho1220*L/A
A = area of cross section = pi*r^2 = pi*(0.083*10^-3)^2
L = Rt*A/rho1220
L = 157.1* pi*(0.083*10^-3)^2/(3.584*10^-7) = 9.49 m <<<--------ANSWER
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