ENV_Assign1_Solutions

ENV_Assign1_Solutions - P H Y S1 0 0 4 P h y s i c s 1 E n...

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PH YS1004 Phy s i c s 1 (Environm e ntal) Solution s to A ss ignm e nt 1 (El ec tri c ity & Magn e ti s m) Charging a Condu c ting Rod D e s c ription: This problem explores the behaviour of charge on conductors This problem explores the behaviour of charge on conductors. We take as an example a long conducting rod suspended by insulating strings. Assume that the rod is initially electrically neutral. For convenience we will refer to the left end of the rod as end A, and the right end of the rod as end B. In the answer options for this problem, "strongly attracted/repelled" means "attracted/repelled with a force of magnitude similar to that which would exist between two charged balls. Part A A small metal ball is given a negative charge, then brought near (i.e., within about 1/10 the length of the rod) to end A of the rod. What happens to end A of the rod when the ball approaches it closely this first time? 1. It is strongly repelled. 2. It is strongly attracted. 3. It is weakly attracted. 4. It is weakly repelled. 5. It is neither attracted nor repelled. An s w e r Option 2 is correct. The rod is a conductor and charge will separate within the rod leaving a net positive charge at the left and a net negative charge on the right. The negative charge of the ball and the negative charge of the left end of the rod will strongly attract. This charge is said to be "induced" by the presence of the electric field of the charged ball: It is not transferred by the ball.
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Now c on s id e r what happ e n s wh e n th e s mall m e tal ball i s r e p a t dly giv e n a n e gativ e c harg e and th e n brough in o c on with e nd A of th e rod . Part B After a great many contacts with the charged ball, how is the charge on the rod arranged (when the charged ball is far away)? 1. There is positive charge on end B and negative charge on end A. 2. There is negative charge spread evenly on both ends. 3. There is negative charge on end A with end B remaining neutral. 4. There is positive charge on end A with end B remaining neutral. An s w r Option 2 is correct. After repeated contacts the negative charge on the ball flows to neutralize the positive charge on the left end of the rod. This leaves the rod with a net negative charge which will distribute itself evenly over the rod. Part C How does end A of the rod react when the charged ball approaches it after a great many previous contacts with end A? Assume that the phrase "a great many" means that the total charge on the rod dominates any charge movement induced by the near presence of the charged ball. 1. It is strongly repelled. 2. It is strongly attracted. 3. It is weakly attracted. 4. It is weakly repelled. 5. It is neither attracted nor repelled. The ball is still charged and the rod has a net negative charge. Hence the two will strongly repel each other. Option 1 is correct.
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ENV_Assign1_Solutions - P H Y S1 0 0 4 P h y s i c s 1 E n...

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