Exam 2 - 07 - Solutions

# Exam 2 - 07 - Solutions - Physics 152 Practice Exam(from...

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Physics 152 Practice Exam (from Prof. Donoghue, 2007. This was designed as a practice exam, not as a real exam.) The answers are given on the last page. 1. A rod of 2.0-m length and a square (2.0 mm × 2.0 mm) cross section is made of a material with a resistivity of 6.0 × 10 –8 Ω m. If a potential difference of 0.50 V is placed across the ends of the rod, at what rate is heat generated in the rod? a. 3.0 W b. 5.3 W c. 8.3 W d. 1.3 W e. 17 W 2. What is the current in the 10- Ω resistor ? + 21 V 10 Ω 5 Ω 5 Ω 5 Ω a. 0.60 A b. 3.0 A c. 1.2 A d. 2.4 A e. 0.30 A 3. If I = 0.40 A in the circuit segment shown below, what is the potential difference V a V b ? a b 12 Ω 8 Ω 10 Ω 10 Ω I a. 31 V b. 28 V c. 25 V d. 34 V e. 10 V

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4. What is the equivalent resistance between points a and b when R = 12 Ω ? R R R R R R b a a. 20 Ω b. 16 Ω c. 24 Ω d. 28 Ω e. 6.0 Ω 5. If R = 2.0 k Ω , C = 4.0 mF, Ε = 8.0 V, Q = 20 mC, and I = 3.0 mA, what is the potential difference V b V a ? R E I + + Q C a b + a. +7.0 V b. +19 V c. +9.0 V d. –3.0 V e. –14 V 6. Which of the following are correct relations for the circuit shown? Mark ALL that apply! a. I 1 = I 2 + I 3 b. V 1 – I 1 R 1 – I 3 R 3 = 0 c. V 2 – I 2 R 2 – I 3 R 3 = 0 d. V 1 – I 1 R 1 – I 2 R 2 + V 2 = 0 e. I 1 R 1 = I 2 R 2 + I 3 R 3
7. At t = 0 the switch S is closed with the capacitor uncharged. If C = 50 μ F, Ε = 20 V, and R = 4.0 k Ω , what is the current in the resistor when t = 0.3 sec? R + E C + + Q S I a. 5.0 x 10 -3 A b. 2.3 x 10 -3 A c. 1.7 x 10 -3 A d. 1.1 x 10 -3 A e. 0.5 x 10 -3 A 8. In an RC circuit, how many time constants must elapse if an initially uncharged capacitor is to reach 80% of its final potential difference?

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## This note was uploaded on 09/06/2011 for the course PHYSICS 152 taught by Professor Brar during the Spring '08 term at UMass (Amherst).

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Exam 2 - 07 - Solutions - Physics 152 Practice Exam(from...

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