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Formative assessment questions for teaching physics

A2L Item 202

  • Description: Indicate the configurations of uniformly charged rods for which the electric field at the origin has non-zero components in both the x and y directions.
  • Goal: Reason regarding electric fields
  • Source: 283-11, E at origin due to charged rods
  • Keywords: Distributed Charges, Electric Field, Electromagnetism, Vectors

The question for students:

For which of the configuration(s) below does the total electric field vector at the origin have non-zero components in both the x and y directions?

Item202_fig1.gif

  1. 2 only
  2. 1 and 3 only
  3. 5 only
  4. 4 only
  5. 1 and 5 only
  6. None of the above

Commentary for teachers:

Answer

(6) Only situation 3 meets the condition. A good exercise is to have students draw the contribution to the field at the origin due to each rod. The contributions should have the correct relative size and direction.