Physics 2 - gilvin (jg47854) 11. Capacitance meyers (21235)...

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Unformatted text preview: gilvin (jg47854) 11. Capacitance meyers (21235) 1 This print-out should have 18 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. This homework is due Friday, March 11, at midnight Tucson time. 001 (part 1 of 2) 10.0 points A 3 . 47 F capacitor is connected to a 16 V battery. What is the charge on each plate of the capacitor? Correct answer: 55 . 52 C. Explanation: Let : C = 3 . 47 F = 3 . 47 10 6 F and V 1 = 16 V . q = C V 1 = (3 . 47 10 6 F) (16 V) 10 6 C 1 C = 55 . 52 C . 002 (part 2 of 2) 10.0 points If this same capacitor is connected to a 3 V battery, what charge is stored? Correct answer: 10 . 41 C. Explanation: Let : V 2 = 3 V . The charge is q = C V 2 = (3 . 47 10 6 F) (3 V) 10 6 C 1 C = 10 . 41 C . 003 10.0 points A parallel plate capacitor is connected to a battery. + Q Q d b b 2 d b b If we double the plate separation, 1. the charge on each plate is halved. cor- rect 2. the electric field is doubled. 3. the capacitance is doubled. 4. the potential difference is halved. 5. None of these. Explanation: The capacitance of a parallel plate capaci- tor is C = A d . Hence doubling d halves the capacitance, and Q = C V is also halved parenleftbigg C = A 2 d = 1 2 A d = 1 2 C parenrightbigg . 004 10.0 points A parallel-plate capacitor has a capacitance C . A second parallel-plate capacitor has plates with twice the area and twice the sepa- ration. The capacitance of the second capacitor is most nearly 1. 1 2 C . 2. 2 C . 3. C . correct gilvin (jg47854) 11. Capacitance meyers (21235) 2 4. 1 4 C . 5. 4 C . Explanation: C = A d = 2 A 2 d = A d = C . 005 (part 1 of 2) 10.0 points Consider Earth and a cloud layer 780 m above Earth to be the plates of a parallel-plate ca- pacitor. The permittivity of free space is 8 . 85419 10 12 C 2 / N m 2 . If the cloud layer has an area of 0 . 7 km 2 = 7 10 5 m 2 , what is the capacitance? Correct answer: 7 . 94607 10 9 F. Explanation: Let : A = 0 . 7 km 2 = 7 10 5 m 2 , h = 780 m and = 8 . 85419 10 12 C 2 / N m 2 . The capacitance of the cloud layer is C = A h = ( 8 . 85419 10 12 C 2 / N m 2 ) parenleftbigg 7 10 5 m 2 780 m parenrightbigg = 7 . 94607 10 9 F . 006 (part 2 of 2) 10.0 points If an electric field strength greater than 3 10 6 N / C causes the air to break down and conduct charge (lightning), what is the maximum charge the cloud can hold? Correct answer: 18 . 5938 C. Explanation: Let : E max = 3 10 6 N / C . The maximum charge is Q max = C V max = C E max h = (7 . 94607 10 9 F) (3 10 6 N / C) (780 m) = 18 . 5938 C ....
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This note was uploaded on 04/29/2011 for the course PHYS 202 taught by Professor Doc during the Spring '11 term at North Texas.

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Physics 2 - gilvin (jg47854) 11. Capacitance meyers (21235)...

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