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A2L Item 127

Meta-Information
Description: 
Given configurations of Gaussian surfaces and electric field lines, identify the situations having non-zero flux.
Goal: 
Link flux to field lines.
Level: 
Undergraduate
Keywords: 
Electromagnetism
Keywords: 
Flux
Source: 
283-415 nonzero flux?

The circles in the picture below are Gaussian surfaces. All other lines are electric field lines. For which cases is the flux non-zero?

  1. a
  2. a, b, and f
  3. a, b, e, and f
  4. a, b, d, e, and h
  5. a and b
  6. All but g
  7. All of them
  8. None of the above
  9. Cannot be determined
Commentary

Answer

(2) As “follow-up” it is good to ask questions about comparisons between two or more of the situations. For example, which is flux is larger, a or f? Such questions help determine what students are focused upon; are they keying on number of lines, do they understand that the flux can be negative.