Introduction / Context:
Permeability measures how easily a material supports the formation of magnetic flux. Understanding how different classes of materials respond to an applied magnetic field is fundamental in electromagnetics and transformer/core design. This item asks which class has the lowest permeability relative to free space (μ0).
Given Data / Assumptions:
- Classes considered: diamagnetic, paramagnetic, ferromagnetic.
- Relative permeability μr = μ / μ0.
- We compare typical trends, not rare edge cases or extreme temperatures.
Concept / Approach:
- Diamagnetic: weakly repelled by magnetic fields; induced magnetization opposes applied field → μr slightly less than 1.
- Paramagnetic: weak attraction; μr slightly greater than 1.
- Ferromagnetic: strong attraction and domain alignment; μr » 1, often hundreds to thousands.
Step-by-Step Reasoning:
Identify trend: μr(diamagnetic) < 1 < μr(paramagnetic) < μr(ferromagnetic).Therefore the lowest permeability occurs in diamagnetic materials because their response reduces net flux relative to free space.Examples: bismuth, copper, gold, and water are weakly diamagnetic; iron and steel are ferromagnetic with very high μ.
Verification / Alternative check:
Check with sorting/induction experiments: diamagnetic samples are weakly expelled from strong field regions, consistent with μr < 1.
Why Other Options Are Wrong:
- A paramagnetic material: μr slightly > 1, not the lowest.
- A ferromagnetic material: μr » 1, the highest class among the three.
- All of the above / None of the above: Contradict the established ordering of μr.
Common Pitfalls:
- Confusing susceptibility sign (χ < 0 for diamagnetism) with magnitude; the key is μr relative to 1.
- Assuming 'weak' always means 'lowest' across all classes without recalling μr positions.
Final Answer:
A diamagnetic material
Discussion & Comments