Question 1

What is Gauss's law?

Accepted Answer

Gauss's law states that the net electric flux through any closed surface equals the total charge enclosed divided by ε₀. The law remains valid even when the surface is not spherical or has an irregular shape.

Question 2

Why is a spherical Gaussian surface used for a central point charge?

Accepted Answer

Spherical symmetry makes the electric field have the same magnitude everywhere on the chosen sphere and point radially outward or inward. Therefore the flux becomes E times the sphere's area, giving E = kQ/r².

Question 3

What is the electric field due to an infinite uniformly charged sheet?

Accepted Answer

The field magnitude is E = σ/(2ε₀), where σ is the surface charge density. It is perpendicular to the sheet, points away from a positive sheet and toward a negative sheet, and is independent of distance from the sheet.

Question 4

Why does only the two caps contribute in the pillbox argument?

Accepted Answer

The electric field of the infinite sheet is parallel to the curved wall of the pillbox, so the field has no component normal to that wall. The field is perpendicular to the two flat caps, whose combined flux has magnitude 2EA; the signed result is +2EA for a positive sheet and −2EA for a negative sheet.

Question 5

What is the field inside and outside a uniformly charged thin spherical shell?

Accepted Answer

For a concentric Gaussian sphere entirely inside the shell, no charge is enclosed, so the field is zero throughout the interior. Outside the shell, the total charge Q is enclosed and the field is E = kQ/r², just like a point charge at the centre.

Gauss's Law by Symmetry: Fields of the Sheet & the Shell

About this lab

Practice