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25_Ch 17 College Physics ProblemCH17 Current and Resistance

# 25_Ch 17 College Physics ProblemCH17 Current and Resistance...

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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 v I nq = ( ) A , the density of free electrons is ( )( ) ( ) 2 2 4 19 150 A 3.17 10 m s 1.60 10 C 5.00 10 m d I n v e r π π = = × × × 3 or 28 3 3.77 10 m n = × 17.58 At temperature T , the resistance of the carbon wire is ( ) 0 0 1 c c c R R T T α = + , and that of the nichrome wire is ( ) 0 1 n n n R R T T α 0 = + ( ) . When the wires are connected end to end, the total resistance is ( )( ) 0 T 0 0 0 0 c n c c n n R R R α α + + + k c n R R R R T = + = If this is to have a constant value of 10.0 as the temperature changes, it is necessary that (1) and 0 0 10.0 k c n R R + = 0 0 0 c c n n R R α α + ( ) 10.0 k 0.4 Ω − = 0 0 10.0 k c n R R = Ω − ( ) 0 0 0.50 10 C n n R × ° + (2) From equation (1), , and substituting into equation (2) gives
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