A Tube with a 3

Multiple Choice

A tube with a 3.0-mm radius has ions flowing through it along its length. To determine the rate at which the charge is being moved through the tube, the magnetic field just outside the tube is measured and found to be If the only contributor to the magnetic field is the moving ions, and if the walls of the container are very thin and do not screen magnetism, what is the magnitude of the current flowing through the tube? (μ₀ = 4π × 10^-7 T ∙ m/A)

A) 66 A
B) 132 A
C) 829 A
D) 415 A