A long solenoid produces a magnetic flux density of 2.5 mT in its center when no core…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A long solenoid produces a magnetic flux density of 2.5 mT in its center when no core is present. Three solid cylindrical cores—X, Y, and Z—of identical dimensions are inserted, one at a time, while the solenoid current is kept constant. The measured flux densities inside the solenoid are
• Core X: 2.4 mT
• Core Y: 3.0 mT
• Core Z: 25 mT
(a) Assuming the magnetizing field produced by the solenoid is unchanged by the insertion of a core, calculate the relative permeability μr of each core.
(b) Classify each core as diamagnetic, paramagnetic, or ferromagnetic based on your calculations.
(c) If all three cores are removed from the solenoid after the current is switched off, which core, if any, would be expected to exhibit a persistent magnetic field? Explain your reasoning.