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Formative assessment questions for teaching physics

A2L Item 135

  • Description: Select the situation for which the movement of a negative charge through an electric field results in the greatest increase of potential energy.
  • Goal: Link electric fields, work and potential energy
  • Source: 283-455 Change in Potential Energy when moving a charge
  • Keywords: Electromagnetism, Potential Energy, Work

The question for students:

In each of the situations below a negative charge is moved along a path from point A to point B in the presence of an electric field, as shown. For which situation is the increase in potential energy the greatest?

Item135_fig1.gif

Commentary for teachers:

Answer

(2) In case 1 the charge moves to a lower potential energy. In case 3 the charge returns to a point having the same distance to the plane of charge as it originally had, meaning no net work. In case 4 the charge moves along an equipotential and no work is done. Students should be asked to identify the charge configuration that could account for each of these field situations. They can also be asked for which case is the electrostatic potential change the greatest.