Ampere's Law: a Long, Straight Wire with Current Flowing

Ampere's law: A long, straight wire with current flowing through it produces magnetic field strength at its surface. If the wire has a radius R, where within the wire is the field strength equal to of the field strength at the surface of the wire? Assume that the current density is uniform throughout the wire. (μ₀ = 4π × 10^-7 T ∙ m/A)

A) 0.36 R
B) 0.060 R
C) 0.64 R
D) 0.030 R