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Unformatted text preview: Husain, Zeena Homework 2 Due: Feb 3 2004, 4:00 am Inst: Sonia Paban 1 This printout should have 24 questions. Multiplechoice questions may continue on the next column or page find all choices before making your selection. The due time is Central time. 001 (part 1 of 1) 10 points 1) Two uncharged metal balls, X and Y , each stand on a glass rod and are touching. Y X 2) A third ball carrying a positive charge, is brought near the first two. Y X + 3) While the positions of these balls are fixed, ball X is connected to ground. Y X + 4) Then the ground wire is disconnected. Y X + 5) While X and Y remain in touch, the ball carring the positive charge is removed. Y X 6) Then ball X and Y are separated. Y X After these procedures, the signs of the charge q X on X and q Y on Y are 1. q X is negative and q Y is neutral. 2. q X is positive and q Y is negative. 3. q X is positive and q Y is neutral. 4. q X is neutral and q Y is negative. 5. q X is neutral and q Y is neutral. 6. q X is positive and q Y is positive. 7. q X is negative and q Y is positive. 8. q X is neutral and q Y is positive. 9. q X is negative and q Y is negative. cor rect Explanation: When the ball with positive charge is brought nearby, the free charges inside X and Y rearrange themselves. The negative charges are attracted and go to the right ( i.e. move to Y ), whereas the positive charges are repelled and collect in the left hand side of the system XY , i.e., in X . When we ground X , the positive charges which have collected in X are allowed to es cape (they strive to the left), whereas the negative charges in Y are still held enthralled by the positive charge on the third ball. We break the ground. Now we remove the third ball with positive charge. The charge on Y is redistributed in the system XY , i.e. they share the negative charge (equally if identical). Finally we separate X and Y . The signs of the charge on X and that on Y are both negative. Husain, Zeena Homework 2 Due: Feb 3 2004, 4:00 am Inst: Sonia Paban 2 002 (part 1 of 1) 10 points A rod 19 . 5 cm long is uniformly charged and has a total charge of 13 . 2 C. Determine the magnitude of the electric field along the axis of the rod at a point 25 . 0685 cm from the center of the rod. Correct answer: 2 . 22428 10 6 N / C. Explanation: Given : = 19 . 5 cm , Q = 13 . 2 C , and r = 25 . 0685 cm . For a rod of length and linear charge density (charge per unit length) , the field at a dis tance d from the end of the rod along the axis is E = k e Z d + d x 2 dx = k e x fl fl fl fl d + d = k e d ( + d ) , where dq = dx . The linear charge density (if the total charge is Q ) is = Q so that E = k e Q d ( + d ) = k e Q d ( + d ) ....
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 Spring '08
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