Question

For an infinite line charge with linear charge density λ, which Gaussian surface is most appropriate?

Options

• A concentric sphere centered at the line

• An irregular shaped closed surface

• A pillbox perpendicular to the line

• A co-axial cylinder with the line as its axis

Answer 1

For an infinite line charge with linear charge density λ, a co-axial cylinder (cylinder whose axis coincides with the line charge) is the ideal Gaussian surface. The cylindrical symmetry ensures that the electric field is uniform and perpendicular to the curved surface, and parallel to the flat ends, making calculations straightforward.