25 - CURRENT, RESISTANCE, AND ELECTROMOTIVE FORCE 25 25.4....

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C URRENT , R ESISTANCE , AND E LECTROMOTIVE F ORCE 25.4. (a) IDENTIFY: By definition, J = I/A and radius is one-half the diameter. SET UP: Solve for the current: I = JA = J π( D /2) 2 EXECUTE: I = (1.50 10 6 A/m 2 )( π )[(0.00102 m)/2] 2 = 1.23 A EVALUATE: This is a realistic current. (b) IDENTIFY: The current density is J = nqv d SET UP: Solve for the drift velocity: v d = J/nq EXECUTE: Since most laboratory wire is copper, we use the value of n for copper, giving 62 d (1.50 10 A/m ) v /[(8.5 10 28 el/m 3 )(1.60 19 10 C) = 1.1 4 10 m/s = 0.11 mm/s EVALUATE: This is a typical drift velocity for ordinary currents and wires. 25.16. IDENTIFY: Apply L R A and solve for L . SET UP: 2 /4 AD , where 0.462 mm D . EXECUTE: 32 8 (1.00 )( 4)(0.462 10 m) 9.75 m. 1.72 10 m RA L EVALUATE: The resistance is proportional to the length of the wire. 25.24. IDENTIFY: Apply L R A and V IR . SET UP: 2 Ar EXECUTE: 42 7 (4.50 V) (6.54 10 m) 1.37 10 m. (17.6 A)(2.50 m) RA VA L IL EVALUATE: Our result for shows that the wire is made of a metal with resistivity greater than that of good metallic conductors such as copper and aluminum.
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This note was uploaded on 10/25/2010 for the course PHYS 260 taught by Professor Hkmiet during the Spring '08 term at George Mason.

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25 - CURRENT, RESISTANCE, AND ELECTROMOTIVE FORCE 25 25.4....

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