Lab 4 Electric Potentials & Fields

Lab 4 Electric Potentials & Fields - Physics 1BL...

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Physics 1BL Spring 2009 1 Pre-Lab Activity The diagram represents a contour map of a hilly island. Copy it into your lab notebook. The outer contour of the figure is at sea level. All points on any one particular contour line are at the same elevation (vertical distance above sea-level). The distance between any two contour lines in the diagram represents the horizontal distance between points on the two different contours. North is up. 1. Each contour line as you go inland represents ground that is at a constant elevation 5 meters higher than the previous contour. a) At what points on the map are there steep cliffs? Show at least three places. b) There are two high areas, label the eastern one A and the western one B. How high are they? c) Mark a straight-line path to climb from sea level to the high point B with the most gentle slope. d) You are interested in how much work it takes to lift your body mass from sea level to the B peak. If you follow the path you chose in part c) will you minimize the amount of work to climb to the top, or will it make no difference? 2. The same diagram could also represent the contours of the electrical potential of two positively charged objects with irregular shapes (for example charges stored on a rubber sheet). Assume that the outer part of the figure is at zero potential. Each contour line going towards the center represents an equipotential surface with a potential 5 V greater than the previous contour. a) Where is the electric field particularly strong? Show at least three places. Explain your reasoning with reference to Q1(a). b) Where are the two highest charge densities? Explain your reasoning. c) What path would require you to use the least amount of force to push a test charge from zero potential to the point of highest potential of one of the charged objects? (Choose the same one you labeled B in 1b) above.) Explain your reasoning. d) Would you actually do less work to move the test charge from 0 V to the voltage at B by using the path selected in 2c), or would the actual path make no difference? 3. An electron is released from rest at point B (as shown to the right), where the potential is 0 V. Afterward, the electron (choose one of the following and defend your choice): a) Remains at rest at B. b) Moves toward C with a steady speed. c) Moves toward C with an increasing speed. d) Moves toward A with a steady speed. e) Moves toward A with an increasing speed.
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Physics 1BL Spring 2009 2 Group Activity: Copy the three charge configurations shown below to your whiteboard. For each configuration, first draw what you would expect the electric field lines to look like. Then, draw the corresponding equipotential surfaces from the field lines you just drew. Once you finish, ask your TA to look over your work, as it is essential for the rest of the lab that you understand the relation between electric field lines and equipotential surfaces. You will be performing the
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Lab 4 Electric Potentials & Fields - Physics 1BL...

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