Two of Maxwell's equations contain an integral over a closed surface. For them the infinitesimal vector area is always:

Question

Two of Maxwell's equations contain an integral over a closed surface. For them the infinitesimal vector area  is always:

Quizplus · Accepted Answer

According to the divergence theorem, the integral over a closed surface of the divergence of a vector field is equal to the volume integral of the same vector field over the region enclosed by the closed surface. This requires the infinitesimal vector area to be perpendicular to the surface and pointing outward. Therefore, for the two Maxwell's equations that involve an integral over a closed surface (Gauss's law and Ampere's law with displacement current), the infinitesimal vector area is always perpendicular to the surface and pointing outward.

Two of Maxwell's Equations Contain an Integral Over a Closed