To practice Problem-Solving Strategy 24.1 Magnetic field problems.
The element niobium, which is a metal, is a superconductor at temperatures below 9 K . This means that at such low temperatures a niobium wire has no electrical resistance. The superconductivity of the wire, however, is destroyed if the magnetic field at the surface of the wire exceeds 0.10 T . What is the maximum current in a straightsuperconducting niobium wire of radius 1.5 mm ? You may assume that all the current flows in the center of the wire.
Prepare
Create a visual representation of the problem. First choose the best orientation for the wire, then draw the magnetic field created by the current. You can then determine your known variables and identify those that you must find.
Recall that you are to treat the current as if it all runs through the center of the wire, and you are interested in the value of the magnetic field at the surface of the wire. Sort the following variables as known or unknown: the magnitude of the magnetic field B, the current I, and the distance r between the current and the point at which the magnetic field has a value of B.