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Unformatted text preview: duong (ktd359) – Homework 1 – Spurlock – (44203) 1 This printout should have 53 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A negatively charged balloon has 4 . 2 μ C of charge. How many excess electrons are on this bal loon? Correct answer: 2 . 625 × 10 13 electrons. Explanation: Let : q = − 4 . 2 μ C and ρ = − 1 . 60 × 10 − 19 C / electron . The charge density is ρ = q N N = q ρ = − 4 . 2 × 10 − 6 C − 1 . 6 × 10 − 19 C / electron = 2 . 625 × 10 13 electrons . 002 10.0 points Two electrons in an atom are separated by 1 . 7 × 10 − 10 m, the typical size of an atom. What is the force between them? The Coulomb constant is 9 × 10 9 N · m 2 / C 2 . Correct answer: 7 . 99226 × 10 − 9 N. Explanation: Let : d = 1 . 7 × 10 − 10 m and k e = 9 × 10 9 N · m 2 / C 2 . The force between the electrons is F = k e q 1 q 2 d 2 = k e q 2 e d 2 = 9 × 10 9 N · m 2 / C 2 1 . 7 × 10 − 10 m 2 × (1 . 602 × 10 − 19 C) 2 = 7 . 99226 × 10 − 9 N . 003 10.0 points Two identical positive charges exert a repul sive force of 6 . 5 × 10 − 9 N when separated by a distance 4 × 10 − 10 m. Calculate the charge of each. The Coulomb constant is 8 . 98755 × 10 9 N · m 2 / C 2 . Correct answer: 3 . 4017 × 10 − 19 C. Explanation: Let : F = 6 . 5 × 10 − 9 N , d = 4 × 10 − 10 m , and k e = 8 . 98755 × 10 9 N · m 2 / C 2 . The electric force is F e = k e q 1 q 2 d 2 d 2 F e k e = q 2 q = radicalBigg d 2 F k e = d radicalbigg F e k e = (4 × 10 − 10 m) × radicalBigg 6 . 5 × 10 − 9 N 8 . 98755 × 10 9 N · m 2 / C 2 = 3 . 4017 × 10 − 19 C . 004 (part 1 of 2) 10.0 points Two point charges are separated by 5 cm, with an attractive force between them of 26 N. Find the force between them when they are separated by 12 cm. The Coulomb constant is 8 . 99 × 10 9 N · m 2 / C 2 . Correct answer: 4 . 51389 N. Explanation: Let : d 1 = 5 cm , F 1 = 26 N , and d 2 = 12 cm . duong (ktd359) – Homework 1 – Spurlock – (44203) 2 The force between two point charges is F = k q 1 q 2 r 2 ∝ 1 r 2 , so F 2 F 1 = r 2 1 r 2 2 F 2 = F 1 r 2 1 r 2 2 = (26 N) (5 cm) 2 (12 cm) 2 = 4 . 51389 N . 005 (part 2 of 2) 10.0 points If the two charges have equal magnitude, what is the magnitude of each charge for the origi nal force of 26 N? Correct answer: 2 . 68891 × 10 − 6 C. Explanation: Let : d 1 = 5 cm , F 1 = 26 N , q = q 1 = q 2 , and k = 8 . 99 × 10 9 N · m 2 / C 2 . The force between the two point charges is F = k q 2 r 2 q = radicalbigg F r 2 k = radicalBigg (26 N) (5 cm) 2 8 . 99 × 10 9 N · m 2 / C 2 = 2 . 68891 × 10 − 6 C . This could also be determined using the second force and its corresponding distance....
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This note was uploaded on 03/26/2012 for the course PHYS 1442 taught by Professor O'donnell during the Spring '08 term at UT Arlington.
 Spring '08
 O'donnell
 Charge, Work

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