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hw10_solns

# hw10_solns - Answer Key Homework 10 David McIntyre This...

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Answer, Key – Homework 10 – David McIntyre 1 This print-out should have 22 questions, check that it is complete. Multiple-choice questions may continue on the next column or page: find all choices before making your selection. The due time is Central time. Chapter 26 problems. 001 (part 1 of 1) 0 points A parallel-plate capacitor is charged by con- necting it to a battery. If the battery is disconnected and the sep- aration between the plates is increased, what will happen to the charge on the capacitor and the electric potential a cross it? 1. The charge increases and the electric po- tential decreases. 2. The charge decreases and the electric po- tential increases. 3. The charge and the electric potential in- crease. 4. The charge decreases and the electric po- tential remains fixed. 5. The charge and the electric potential de- crease. 6. The charge remains fixed and the electric potential increases. correct 7. The charge and the electric potential re- main fixed. 8. The charge increases and the electric po- tential remains fixed. 9. The charge remains fixed and the electric potential decreases. Explanation: Charge is conserved, so it must remain con- stant since it is stuck on the plates. With the battery disconnected, Q is fixed. C = ² A d A larger d makes the fraction smaller, so C is smaller. Thus the new potential V 0 = Q C 0 is larger. 002 (part 1 of 2) 5 points Given: A capacitor network is shown below. 116 V 14 μ F 20 μ F 7 μ F a b Find the equivalent capacitance C ab be- tween points a and b for the group of ca- pacitors. Correct answer: 15 . 2353 μ F. Explanation: Given : C 1 = 14 μ F , C 2 = 20 μ F , C 3 = 7 μ F , and E B = 116 V . E B C 1 C 2 C 3 a b The capacitors C 1 and C 2 are in series, so C s = 1 C 1 + 1 C 2 - 1 = C 1 C 2 C 1 + C 2 . C s is parallel with C 3 , so C ab = C s + C 3 = C 1 C 2 C 1 + C 2 + C 3 = (14 μ F) (20 μ F) 14 μ F + 20 μ F + 7 μ F = 8 . 23529 μ F + 7 μ F = 15 . 2353 μ F .

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Answer, Key – Homework 10 – David McIntyre 2 003 (part 2 of 2) 5 points What charge is stored on the 7 μ F capacitor on the lower portin of the parallel circuit? Correct answer: 812 μ C. Explanation: Since C s and C 3 are parallel, the same po- tential E B = V is across both, so q 3 = C 3 V = (7 μ F) (116 V) = 812 μ C . 004 (part 1 of 2) 5 points Four capacitors are connected as shown in the figure. 21 μ F 68 μ F 35 μ F 84 μ F 97 V a b c d Find the capacitance between points a and b .
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