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Unformatted text preview: oliver (jmo673) HW03 Tsoi (59090) 1 This printout should have 24 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 4) 10.0 points For the configuration shown in the figure, sup pose that a = 7 cm, b = 21 cm, and c = 28 cm. Furthermore, suppose that the electric field at a point 10 cm from the center is measured to be 4400 N / C radially inward while the elec tric field at a point 40 cm from the center is 260 N / C radially outward. a b c b Insulator Conductor Find the charge on the insulating sphere. Correct answer: 4 . 89566 10 9 C. Explanation: Let : a = 7 cm , b = 21 cm , c = 28 cm , r 1 = 10 cm = 0 . 1 m , and E 1 = 4400 N / C , Basic Concept: E = 0 inside conductors, Gauss Law: contintegraldisplay vector E d vector A = Q Solution: By Gauss Law, E 2 ( 4 r 2 1 ) = q , where q is the charge contained in the insulat ing sphere, so q = E 2 ( 4 r 2 1 ) = (4400 N / C) bracketleftbig 4 (0 . 1 m) 2 bracketrightbig (8 . 85419 10 12 C 2 / N m 2 ) = 4 . 89566 10 9 C , where E is negative because it points radially inward . 002 (part 2 of 4) 10.0 points Find the net charge on the conducting sphere. Correct answer: 9 . 52428 10 9 C. Explanation: Let : r 2 = 40 cm = 0 . 4 m and E 2 = 260 N / C . Similarly, by Gauss Law, the electric field at r = r 2 , where r 2 > c , will be related to the to tal charge enclosed by a concentric Gaussian sphere of radius r 2 . If we call the total charge on the spherical shell Q , Gauss Law is E 2 (4 r 2 2 ) = Q + q , from which we find Q = E 2 ( 4 r 2 2 )  q = (260 N / C) bracketleftbig 4 (0 . 4 m) 2 bracketrightbig (8 . 85419 10 12 C 2 / N m 2 ) ( 4 . 89566 10 9 C) = 9 . 52428 10 9 C . 003 (part 3 of 4) 10.0 points Find the total charge on the inner surface of the hollow conducting sphere. Correct answer: 4 . 89566 10 9 C. Explanation: Since E = 0 inside a conductor, the to tal charge contained in a concentric Gaussian sphere of radius r in , where b < r in < c , must be zero. From this we know that the total charge on the inner surface of the spherical conducting shell must be Q in = q = 4 . 89566 10 9 C . oliver (jmo673) HW03 Tsoi (59090) 2 004 (part 4 of 4) 10.0 points Find the total charge on the outer surface of the hollow conducting sphere. Correct answer: 4 . 62862 10 9 C. Explanation: To find the total charge on the outer surface of the conductor, Q out , we note that Q out + Q in = Q . Then Q out is Q out = Q Q in = 9 . 52428 10 9 C 4 . 89566 10 9 C = 4 . 62862 10 9 C ....
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This note was uploaded on 10/21/2009 for the course PHY 59090 taught by Professor Tsoi during the Fall '09 term at University of Texas at Austin.
 Fall '09
 TSOI
 Physics

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