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Charges near the origin

Page history last edited by Joe Redish 3 years ago



Three equipotential surfaces associated with a set of source charges which are clustered at the origin are shown in the  figure to the right. The values of potential are given in volts. 


A. How much net charge is at the origin?


B. Add to the figure four arrows, representing the electric field that could be “measured” at each of four points. Place their tails (not the pointy ends) at four different points. The placement, directions and relative lengths of your electric field vectors will be graded for consistency, but  the absolute length of your electric field vectors is not critical.


C. Which of the following is the best characterization of this situation? 


  1. There is one singly ionized potassium nucleus at the origin. (The atomic number of potassium is 19.)
  2. There is one electron at the origin.  
  3. There is one proton at the origin.
  4. There are 25 electrons and 25 protons at the origin.
  5. There are 25 electrons and 50 protons at the origin.
  6. There are 50 electrons and 25 protons at the origin.
  7. There is a small fragment of vibranium at the origin.


D. Which of the curves in the figure (right) most likely represents a measurement of the voltage taken along the vertical line x = 4 nm? 





Bill Dorland 3/1/18

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