Teaching Physics with the Physics Suite Edward F. Redish

Interpreting Gauss

Gauss's law states

where A is a surface and qA is a charge. (Note: You may list any number of these statements including all or none.

A) Which of the following statements are true about the surface A appearing in Gauss's Law?

a. The surface A must be a closed surface (must cover a volume).
b. The surface A must contain all the charges in the problem.
c. The surface A must be a highly symmetrical surface like a sphere or a cylinder.
d. The surface A must be a conductor.
e. The surface A is purely imaginary.
f. The normals to the surface A must all be in the same direction as the electric field on the surface.

B) Which of the following statements are true about the charge qA appearing in Gauss's Law?

a. The charge qA is all the charge lying on the Gaussian surface.
b. The charge qA is the charge lying within the Gaussian surface.
c. The charge qA is all the charge in the problem.
d. The charge qA flows onto the Gaussian surface once the surface is established.
e. The electric field E in the integral on the left of Gauss's law is due only to the charge qA.
f. The electric field E in the integral on the left of Gauss's law is due to all charges in the problem.

Note to the instructor: Some of these selections might seem strange, but I have received them as replies in open ended essay questions from students in calculus-based physics.

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