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Unformatted text preview: Thevalingam, Donald – Homework 28 – Due: May 31 2007, midnight – Inst: Eslami 1 This printout should have 34 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. The due time is Central time. 001 (part 1 of 1) 10 points The current in a wire decreases with time according to the relationship I = (2 . 61 mA) × e a t where a = 0 . 13328 s 1 . Determine the total charge that passes through the wire from t = 0 to the time the current has diminished to zero. Answer in units of C. 002 (part 1 of 1) 10 points A copper wire carries 1 amp of electric cur rent. What kind of charge does the electron flow create in the wire? 1. No charge. 2. Negative 3. Positive 003 (part 1 of 1) 10 points In a fluorescent tube of diameter 4 . 4 cm, 1 . 1 × 10 18 1 / s electrons and 1 × 10 17 1 / s positive ions (with a charge of + e ) flow through a crosssectional each second. What is the current in the tube? Answer in units of A. 004 (part 1 of 5) 10 points A current of 25 A exists in a copper (Cu) wire which has a diameter of 1 mm. Each atom of copper has one conduction band, and the average thermal speed r k T m of an electron is 100000 m / s . The mass den sity of Cu is 8 . 92 g / cm 3 , its molar mass is 63 . 5 g / mol, and Avogadro’s number is 6 . 02214 × 10 23 atoms / mole. The electron mass is 9 . 10939 × 10 31 kg, and the resistivity of copper is 1 . 7 × 10 8 Ω · m. What is the current density? Answer in units of A / m 2 . 005 (part 2 of 5) 10 points What is the density of conduction electrons band of copper? Answer in units of m 3 . 006 (part 3 of 5) 10 points What is the drift velocity of the electrons? Answer in units of m / s. 007 (part 4 of 5) 10 points What is the average time between collisions of the “drifting” electrons with the lattice ions? Answer in units of s. 008 (part 5 of 5) 10 points What is their mean free path in this wire? Answer in units of m. 009 (part 1 of 2) 10 points The quantity of charge passing through a sur face of area 1 . 02 cm 2 varies with time as q = q 1 t 3 + q 2 t + q 3 , where q 1 = 5 . 5 C / s 3 , q 2 = 4 . 4 C / s, q 3 = 8 C, and t is in seconds. What is the instantaneous current through the surface at t = 0 . 9 s? Answer in units of A. 010 (part 2 of 2) 10 points What is the value of the current density at t = 0 . 9 s? Answer in units of A / m 2 ....
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This note was uploaded on 04/05/2010 for the course PHY 52033 taught by Professor Tleva during the Spring '10 term at University of Texas.
 Spring '10
 Tleva

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