25_Chapter 16 HomeworkCH17 Current and Resistance

25_Chapter 16 HomeworkCH17 Current and Resistance - 93...

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Current and Resistance 93 17.57 The current in the wire is 15.0 V 150 A 0.100 V R I == = Then, from d vI n q = () A , the density of free electrons is ( ) ( ) 2 2 41 9 150 A 3.17 10 m s 1.60 10 C 5.00 10 m d I n ve r π −− ××× 3 or 28 3 3.77 10 m n 17.58 At temperature T , the resistance of the carbon wire is ( ) 00 1 cc c RR TT α =+− , and that of the nichrome wire is ( ) 0 1 nn n 0 . When the wires are connected end to end, the total resistance is ( )( ) 0 T 0 0 c n c n R R R αα + + + k cn RR R R T =+= If this is to have a constant value of 10.0 as the temperature changes, it is necessary that (1) and 10.0 k += 0 + 1 0 . 0 k 0 . 4 Ω− = 10.0 k =Ω 0 . 5 01 0 C R  × ° +  (2) From equation (1), , and substituting into equation (2) gives
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