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Homework 4-solutions

Homework 4-solutions - zhou(ejz224 Homework 4 shih(57480...

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zhou (ejz224) – Homework 4 – shih – (57480) 1 This print-out should have 9 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points The current I = a t 2 - b t + c in a section of a conductor depends on time. What quantity of charge moves across the section of the conductor from t = 0 s to t = t 1 ? 1. q = 2 a t 2 1 - b t 1 2. q = a 3 t 3 1 - b 2 t 2 1 + c t 1 correct 3. q = 2 a t 1 - b 4. q = a t 3 1 - b t 2 + c t 1 5. q = 2 a t 2 1 - 3 b t 1 + c t 1 6. q = 3 a t 2 1 - b + c 7. q = a t 3 1 - b 2 t 2 1 + ct 1 8. q = a 3 t 3 1 - b 2 t 2 1 + c 9. q = 3 a t 2 1 - 2 b t 1 + c 10. q = a t 2 1 - b t 1 + c Explanation: The unit of current is Coulomb per second I = d q dt or dq = I dt . To find the total charge in coulombs that passes through the conductor, one must inte- grate the current over the time interval. q = integraldisplay t 1 0 dq = integraldisplay t 1 0 I dt = integraldisplay t 1 0 ( a t 2 - b t + c ) dt = bracketleftbigg a 3 t 3 1 - b 2 t 2 1 + c t bracketrightbigg vextendsingle vextendsingle vextendsingle vextendsingle t 1 0 = a 3 t 3 1 - b 2 t 2 1 + c t 1 . 002 10.0points In a fluorescent tube of diameter 4 . 6 cm, 1 . 3 × 10 18 1 / s electrons and 2 . 3 × 10 18 1 / s positive ions (with a charge of + e ) flow through a cross-sectional each second. What is the current in the tube? Correct answer: 0 . 576 A. Explanation: Let : n electron = 1 . 3 × 10 18 1 / s , n ion = 2 . 3 × 10 18 1 / s , q electron = 1 . 6 × 10 19 C , and q ion = 1 . 6 × 10 19 C . Note that, while the positive and negative charges flow in opposite directions, the total current is their sum: I = I electron + I ion = n electron q electron + n ion q ion = (1 . 3 × 10 18 1 / s) (1 . 6 × 10 19 C) + (2 . 3 × 10 18 1 / s) (1 . 6 × 10 19 C) = 0 . 208 A + 0 . 368 A = 0 . 576 A .

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Homework 4-solutions - zhou(ejz224 Homework 4 shih(57480...

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