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Unformatted text preview: mcconnell (kam2342) – HW 03 – Turner – (60230) 1 This printout should have 14 questions. Multiplechoice questions may continue on the next column or page – find all choices before answering. 001 10.0 points The diagram shows an isolated, positive charge Q , where point B is twice as far away from Q as point A . + Q A B 10 cm 20 cm The ratio of the electric field strength at point A to the electric field strength at point B is 1. E A E B = 4 1 . correct 2. E A E B = 1 1 . 3. E A E B = 8 1 . 4. E A E B = 1 2 . 5. E A E B = 2 1 . Explanation: Let : r B = 2 r A . The electric field strength E ∝ 1 r 2 , so E A E B = 1 r 2 A 1 r 2 B = r 2 B r 2 A = (2 r ) 2 r 2 = 4 . 002 (part 1 of 2) 10.0 points A charge Q is distributed uniformly along the x axis from x 1 to x 2 . The Coulomb constant is 8 . 98755 × 10 9 N · m 2 / C 2 Which of the following integrals is correct for the magnitude of the electric field at x on the x axis? Assume that x > x 2 > x 1 and k e = 1 4 πǫ . 1. integraldisplay x 2 x 1 k e Q ( x 2 x 1 ) x 2 dx 2. integraldisplay x 2 x 1 k e Q ( x 2 x 1 )( x x ) 2 dx correct 3. None of these 4. integraldisplay x 2 x 1 k e Q ( x 2 x )( x x ) 2 dx 5. integraldisplay x 2 x 1 k e Q ( x 2 x ) x 2 dx Explanation: For a continuous charge distribution, dE = k e dq r 2 . Recall that for a uniform linear charge dis tribution, dq = λ dx = Q L dx = Q x 2 x 1 dx . Furthermore, the point x is a distance ( x x ) from a charge element dq . Hence integrating from x = x 1 to x = x 2 yields E = integraldisplay x 2 x 1 k e Q ( x 2 x 1 )( x x ) 2 dx . 003 (part 2 of 2) 10.0 points If x 1 = 0 m, x 2 = 2 . 81 m and the charge Q = 3 . 35 μ C, what is the magnitude E of the electric field at x = 11 . 9 m? Correct answer: 278 . 34 N / C. Explanation: Let : k e = 8 . 98755 × 10 9 N · m 2 / C 2 , x 1 = 0 m , x 2 = 2 . 81 m , x = 11 . 9 m , and Q = 3 . 35 μ C . mcconnell (kam2342) – HW 03 – Turner – (60230) 2 E = integraldisplay x 2 x 1 k e Q ( x 2 x 1 )( x x ) 2 dx = k e Q ( x 2 x 1 )( x x ) vextendsingle vextendsingle vextendsingle vextendsingle x 2 x 1 = ( 8 . 98755 × 10 9 N · m 2 / C 2 ) (2 . 81 m 0 m) × (3 . 35 × 10 6 C) × bracketleftbigg 1 11 . 9 m 2 . 81 m 1 11 . 9 m 0 m bracketrightbigg = 278 . 34 N / C ....
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 Spring '10
 Turner
 Charge, Electric charge, KE, McConnell

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