Question

In which of the following cases does there exist a nonzero magnetic field that can be conveniently determined by using Ampere's law?

a. Outside a point charge that is at rest Inside stationary cylinder carrying uniformly distributed charge b. Inside a very long current-carrying solenoid c. At the center of current-carrying loop of wire d. Outside square current-carrying loop of wire

Answer 1

(C) Has the symmetry for a direct application of Ampere's Law:

B * 2 π * a = μ0 * I

You know the radius a of the loop and I the current in the loop.