A very long,hollow,thin-walled conducting cylindrical shell (like a pipe)of radius R carries a current along its length uniformly distributed throughout the thin shell.Which one of the graphs shown in the figure most accurately describes the magnitude B of the magnetic field produced by this current as a function of the distance r from the central axis?
A) 1
B) 2
C) 3
D) 4
E) 5

Question

A very long,hollow,thin-walled conducting cylindrical shell (like a pipe)of radius R carries a current along its length uniformly distributed throughout the thin shell.Which one of the graphs shown in the figure most accurately describes the magnitude B of the magnetic field produced by this current as a function of the distance r from the central axis? 
A) 1 
B) 2 
C) 3 
D) 4 
E) 5

Quizplus · Accepted Answer

According to Ampere's law, the magnitude of the magnetic field produced by the current in a long, hollow, thin-walled conducting cylinder is proportional to the distance from the central axis. Thus, the graph of the magnetic field strength should be a straight line passing through the origin. 
Option D shows a straight line, which is the correct graph of B as a function of r, therefore, D is the best choice.

A Very Long,hollow,thin-Walled Conducting Cylindrical Shell (Like a Pipe)of Radius