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Worksheet #4 - Solutions

# Worksheet #4 - Solutions - Physics 202 SI Sessions...

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Physics 202 SI Sessions Worksheet #4 Problem 1 The Alaska oil pipeline is approximately 1.27x10 3 km long, 120 cm in diameter, and made of steel with a thickness of about 1.0 cm. Steel has a resistivity of 1.80x10 -7 Ωm. What is the total resistance of the pipeline over its entire length? Answer: R= ρ (l/A) With ρ = 1.80x10 -7 m, l=1.27x10 6 m, and A = ( π d)/4*0.01m= π *0.6m*0.01m/4=0.0377 m 2 , R=6.06 Problem 2 R 1 = ρ (L 1 /A 1 ) R 2 = ρ (L 2 /A 2 ) L 2 = 2*L 1 Total volume is the same V 1 = V 2 A 1 L 1 = A 2 L 2 A 1 = 2A 2 R 2 = ρ (2L 1 /(A 1 /2)) = 4R 1 = 16 Problem 3 A certain toaster has a heating element made of Nichrome resistance wire. When the toaster is first connected to a 120 V source (and the wire is at a temperature of 20.0˚ C), the initial current is 1.80 A. However, the current begins to decease as the resistive element warms up. When the toaster has reached its final operating temperature, the current has dropped to 1.53 A. (a) Find the power the toaster consumes when it is at its operating temperature. (b) What is the final temperature of the heating element? Answer: (a) P=I V =1.53A(120V)=183.6W (b) R=R 0 (1+ α (T-T 0 )), and R= V/I A V A V 8 . 1 120 53 . 1 120 = (1+0.4x10 -3 C -1 (T-20 0 C)) T=461 0 C Problem 4 What is the fractional change in the resistance of an iron filament when its temperature changes from 25.0˚ to 50.0˚ C?

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Worksheet #4 - Solutions - Physics 202 SI Sessions...

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