A long hollow cylindrical conductor (inner radius = 2.0 mm, outer radius = 4.0 mm) carries a current of 12 A distributed uniformly across its cross section. A long wire which is coaxial with the cylinder carries an equal current in the same direction. What is the magnitude of the magnetic field 3.0 mm from the axis?
A) 1.1 mT
B) 1.4 mT
C) 1.7 mT
D) 2.0 mT
E) 0.2 mT

Question

Quizplus · Accepted Answer

The magnetic field inside a long hollow cylindrical conductor is zero. The magnetic field outside the conductor is the same as that of a long straight wire carrying the same current. The magnetic field 3.0 mm from the axis of a long straight wire carrying a current of 12 A is:$$B = \frac{\mu_0 I}{2\pi r} = \frac{(4\pi 	imes 10^{-7} 	ext{ T$\cdot$m/A})(12 	ext{ A})}{2\pi (0.003 	ext{ m})} = 1.1 	ext{ mT}$$

A Long Hollow Cylindrical Conductor (Inner Radius = 2