Direction of induced magnetic dipole moment For atoms or molecules without permanent magnetic moments, the induced magnetic dipole moment produced by an applied magnetic field is in which direction relative to the field?

Difficulty: Easy

Correct Answer: Opposite to the applied field

Explanation:


Introduction / Context:
This question targets basic diamagnetism. In many materials with no permanent dipoles (closed electron shells), an applied magnetic field induces orbital currents that oppose the change in magnetic flux, creating an induced dipole moment.


Given Data / Assumptions:

  • No permanent magnetic moment (diamagnetic response).
  • Weak applied field, linear regime.
  • Atomic/electronic origin of induced magnetism.


Concept / Approach:

Lenz’s law and the classical Langevin viewpoint show that induced currents generate magnetic moments opposing the applied field. Quantum mechanically, Larmor precession leads to an induced magnetic moment antiparallel to the applied field. This universal, weak effect is diamagnetism, present in all materials but usually masked when paramagnetic or ferromagnetic effects exist.


Step-by-Step Solution:

Apply magnetic field B to a closed-shell atom.Induced currents are such that the magnetic moment opposes the field (minimizing energy).Therefore, the induced magnetic dipole is opposite to the applied field direction.


Verification / Alternative check:

Magnetic susceptibility of diamagnets is small and negative, confirming antiparallel induced magnetization (M opposite to H).


Why Other Options Are Wrong:

  • Perpendicular or random orientations contradict the linear diamagnetic response.
  • Along the field corresponds to paramagnetic alignment of permanent moments, not induced diamagnetism.


Common Pitfalls:

Confusing induced diamagnetism with alignment of permanent moments; overlooking that most materials exhibit at least weak diamagnetism.


Final Answer:

Opposite to the applied field

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