Teaching Physics with the Physics Suite

Edward F. Redish

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Orienteering an electric potential

1. (a) The figure on the right shows a contour plot of a piece of a range of hills in Virginia. The outer part of the figure is at sea level (marked 0). Each contour line from the region marked zero shows a level 10 m higher than the previous. The maximum height is 70 m and is shown by the number 70.

Answer the following questions by giving the pair of grid markers (a letter and a number) closest to the point being requested.

  1. Where is there a steep cliff?
  2. Where is there a pass between two hills?
  3. Where is the easiest climb up the hill?

(b) Now suppose the figure represents instead a plot of the electric equipotentials for the surface of a glass plate. The numbers now represent voltage. The maximum is 70 V and each contour line from the region marked zero shows a level 10 V higher than the previous.

  1. Where would a test charge placed on the glass feel the strongest electric force? In what direction would it point?
  2. Is there a place on the glass where a charge could be placed so it feels no electric force? Where?

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Page last modified October 15, 2002: E04