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Unformatted text preview: song (shs546) – Practice HW 7 Solutions – weathers – (22202) 1 This printout should have 12 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A 16 pF capacitor is connected across a 77 V source. What charge is stored on it? Correct answer: 1 . 232 × 10 9 C. Explanation: Let : C = 16 pF = 1 . 6 × 10 11 F and V = 77 V . The capacitance is C = q V q = C V = (1 . 6 × 10 11 F) (77 V) = 1 . 232 × 10 9 C 002 (part 1 of 3) 10.0 points The Coulomb constant is 8 . 98755 × 10 9 N · m 2 / C 2 . If a drop of a conducting liquid had a ca pacitance of 0 . 7 pF in air, what is its radius? Correct answer: 0 . 00629129 m. Explanation: Let : k e = 8 . 98755 × 10 9 N · m 2 / C 2 , C = 0 . 7 pF = 7 × 10 13 F and V = 115 V . If the charge on the drop is Q and its radius is R , then the potential difference between the surface and infinity is V = k e Q R . Thus the capacitance of the drop is C = Q V = R k e R = k e C = ( 8 . 98755 × 10 9 N · m 2 / C 2 ) × (7 × 10 13 F) = . 00629129 m . 003 (part 2 of 3) 10.0 points If its radius is 3 . 2 mm, what is its capacitance? Correct answer: 3 . 56048 × 10 13 F. Explanation: Let : r = 3 . 2 mm = 0 . 0032 m . C = r k e = . 0032 m 8 . 98755 × 10 9 N · m 2 / C 2 = 3 . 56048 × 10 13 F . 004 (part 3 of 3) 10.0 points What is the charge on the smaller drop if its potential is 115 V?...
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This note was uploaded on 04/22/2011 for the course PHYS 2220 taught by Professor Littler during the Spring '00 term at North Texas.
 Spring '00
 Littler

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