AIIMS 2006 Physics Diamagnetism Assertion Reason Question

To analyze the given question regarding diamagnetic materials and their properties, let's break down the assertion and the reason provided.

Assertion:

Diamagnetic materials can exhibit magnetism.

Reason:

Diamagnetic materials have a permanent magnetic dipole moment.

Correct Answer: D) Both Assertion and Reason are false

Explanation:

1. Understanding Diamagnetism:

   • Diamagnetic materials are characterized by their ability to create an opposing magnetic field when exposed to an external magnetic field. This phenomenon is due to the motion of electrons in the material. However, diamagnetic materials do not have a permanent magnetic dipole moment. Instead, their magnetic properties arise only in the presence of an external magnetic field.

2. Assertion Analysis:

   • The assertion states that diamagnetic materials can exhibit magnetism. While it is true that they can exhibit a weak form of magnetism when an external magnetic field is applied, this is not the same as possessing inherent magnetism. Thus, the statement can be misleading, as it implies that diamagnetic materials have a form of magnetism like ferromagnetic materials, which is not the case.

3. Reason Analysis:

   • The reason provided claims that diamagnetic materials have a permanent magnetic dipole moment. This statement is false. Diamagnetic materials do not have permanent magnetic dipole moments; instead, they show induced magnetism. When an external magnetic field is applied, the orbital motion of electrons adjusts to create a very weak opposing magnetic field. When the external field is removed, the induced magnetism disappears.

Clarification of other options:

• Option A: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

  • This is incorrect because both the assertion and reason are false. Diamagnetic materials do not exhibit magnetism in the conventional sense nor do they have a permanent magnetic dipole moment.

• Option B: Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

  • This is also incorrect for the same reasons outlined above. Neither the assertion nor the reason is true.

• Option C: Assertion is true but Reason is false.

  • This option is misleading. The assertion is not true in the context of conventional magnetism, as diamagnetic materials do not exhibit permanent magnetism.

Conclusion:

Thus, the correct answer is D, as both the assertion and reason are false. Diamagnetic materials do not have a permanent magnetic dipole moment, and their magnetic properties only manifest in the presence of an external magnetic field, which does not qualify as exhibiting magnetism in the traditional sense.

Relevant Concepts:

• Diamagnetism is characterized by a negative magnetic susceptibility, which can be mathematically represented as: $\chi_m = -\frac{N \mu^2}{3kT}$ where $\chi_m$ is the magnetic susceptibility, $N$ is the number of magnetic dipoles, $\mu$ is the magnetic moment, $k$ is the Boltzmann constant, and $T$ is the temperature. This relationship highlights that diamagnetic materials respond weakly to magnetic fields and do not maintain a permanent magnetic state.