Electric Flux: Orientation, Surface Integrals, and Geometry

All flashcards

What is electric flux?

A scalar measure of the electric field passing through a surface.

What is the flux through a flat surface in a uniform field?

$\Phi=EA\cos\theta$, where $\theta$ is measured from the surface normal.

What is an area vector?

A vector with magnitude equal to the surface area, directed along a surface normal.

How is the normal chosen for a closed surface?

It points outward everywhere.

What does the circle on a closed-surface integral sign indicate?

Integration over the entire closed surface.

Quiz questions

1. For a uniform electric field through a flat surface, what is the area vector's role in calculating flux?Answer: Its dot product with the field gives the flux: $\Phi=\vec{E}\cdot\vec{A}$.
2. For an open surface, how should its normal direction be selected when calculating signed flux?Answer: Either direction may be chosen, but it must be used consistently.
3. A closed surface encloses no electric charge. What is its net electric flux?Answer: Zero, although flux through individual parts may be nonzero.
4. When is a surface integral generally needed to calculate electric flux?Answer: When the field or the surface normal varies across the surface.
5. A uniform electric field passes through a cube. Why is the net flux zero?Answer: Flux entering one face is canceled by equal flux leaving the opposite face.