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Lesson_3.3_Homework_and_Solutions

Lesson_3.3_Homework_and_Solutions - Lesson 3.3 Homework...

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Lesson 3.3 Homework Solutions 1. A 0.9-V potential difference is maintained across a 1.5 m length of tungsten wire that has a cross-sectional area of 0.6 mm 2 . What is the current in the wire? (6.5 A) Area of cross section of the wire is: A = 0.6 mm 2 = 0.6 × 10 -6 m 2 8 6 1.5 5.5 10 0.1375 0.6 10 0.9 0 5 . 7 6. 13 5 l R A V I R A ρ - - = = × × = × = = = 2. A metal wire of resistance R is stretched to 1.5 times its original length. What is the resistance of the stretched wire? (2.25R) Resistance r of a wire of length L and area of cross section A is: L R A ρ = When the wire is stretched, its volume does not change. If A is the original cross-sectional area and A’ the area of cross section after the stretching, then the original volume = LA Volume after stretching = 1.5L A’ LA = 1.5LA’ ' 1.5 A A = If R’ is the resistance of the stretched wire, 1.5 1.5 ' 2.25 ' / 5 2.25 1. R l l l R A A A ρ ρ ρ = = = = 3. An aluminum rod has a resistance of 1.234 at 20 o C. What will be the resistance of this rod at 120 o C?
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