Difficulty: Easy
Correct Answer: Both A and R are true and R is the correct explanation of A
Explanation:
Introduction / Context:
Ferromagnetic materials exhibit spontaneous magnetization due to aligned spins within microscopic regions called domains. Understanding domains explains hysteresis, coercivity, remanence, and how magnetization changes under applied fields via domain wall motion and rotation.
Given Data / Assumptions:
Concept / Approach:
Domain theory posits that a bulk specimen is partitioned into domains whose magnetizations are individually saturated but differently oriented. Upon applying a field, domains favorably oriented grow at the expense of others, and walls move, producing macroscopic magnetization changes. Bitter powder patterns use fine ferromagnetic particles or colloids that accumulate at stray-field regions near domain walls, making the domain structure visible and thereby providing direct evidence for domains.
Step-by-Step Solution:
Verification / Alternative check:
Modern techniques (Kerr microscopy, Lorentz TEM, MFM) confirm domain structures and dynamics, reinforcing the classical evidence from Bitter patterns.
Why Other Options Are Wrong:
(b) underplays the explanatory link; (c) R is not false; (d) A is not false.
Common Pitfalls:
Assuming individual atomic moments randomly reorient in isolation; in reality, collective domain processes dominate at low to moderate fields.
Final Answer:
Both A and R are true and R is the correct explanation of A
Discussion & Comments