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13_Chapter 17 HomeworkCH17 Current and Resistance

13_Chapter 17 HomeworkCH17 Current and Resistance - Current...

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Current and Resistance 81 (b) At T , the potential difference required to maintain the same current in the copper wire is 200 C = ° ( ) ( ) 0 0 0 0 1 1 R IR T T V T T α α = + = ∆ + ( ) V I = or ( ) ( ) 3 -1 65 mV 1 3.9 10 °C 200 C 20 C + × ° ° 0. V = 1.1 mV = 17.27 (a) The resistance at 20.0°C is ( ) ( ) ( ) 8 0 2 3 1.7 10 m 34.5 m 3.0 0.25 10 m L R A ρ π × Ω⋅ = = = × and the current will be 0 9.0 V 3.0 A 3.0 V I R = = = (b) At 30.0°C, Thus, the current is ( ) ( ) ( ) ( ) ( ) 0 0 1 3 1 3.0 1 3.9 10 C 30.0 C 20.0 C 3.1 R R T T α = + = + × ° ° ° = 9.0 V 2.9 A 3.1 V I R = = = 17.28 The resistance of the heating element when at its operating temperature is
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