CH 17-18 - Current, Resistance, DC Circuits-solutions

# CH 17-18 - Current, Resistance, DC Circuits-solutions -...

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This print-out should have 10 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. 001 10.0 points The mass oF a gold atom is 3 . 27 × 10 - 25 kg. IF 1 . 64 kg oF gold is deposited on the nega- tive electrode oF an electrolytic cell in a period oF 3 . 19 h, what is the current in the cell in this period? Assume that each gold ion carries one elementary unit oF positive charge. Correct answer: 69 . 8752 A. Explanation: Let : m atom =3 . 27 × 10 - 25 kg , m tot =1 . 64 kg , Δ t =3 . 19 h , and q atom =1 . 60 × 10 - 19 C . Δ Q =(numberoFatoms)( q atom ) = m tot m atom · q atom I = Δ Q Δ t I = m tot m atom · q atom Δ t = ± 1 . 64 kg 3 . 27 × 10 - 25 kg ² (1 . 6 × 10 - 19 C) (3 . 19 h)(3600 s / h) = 69 . 8752 A . 002 10.0 points AcurrentoF3A±owsinacopperwire10mm in diameter. The density oF valence electrons in copper is roughly 9 × 10 28 m - 3 . ²ind the driFt speed oF these electrons. Correct answer: 2 . 65258 × 10 - 6 m / s. Explanation: Let : I =3A , r = 10 mm 2 =0 . 005 m , and n e =9 × 10 28 m - 3 . I = j ( πr 2 )= en e v d ( πr 2 ) v d = I en e πr 2 = 3A (1 . 6 × 10 - 19 C) (9 × 10 28 m - 3 ) × 1 π (0 . 005 m) 2 =2 . 65258 × 10 - 6 m / s = 0 . 95493 cm / hours . 003 10.0 points A0 . 78 V potential di³erence is maintained across a 2 m length oF tungsten wire that has ac ro s s - s e c t iona la r eao F0 .

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CH 17-18 - Current, Resistance, DC Circuits-solutions -...

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