Question

Assertion (A) : All atoms have a net magnetic moment. Reason (R) : A current loop does not always behave as a magnetic dipole.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Both Assertion (A) and Reason (R) are false.

Hint:

A current loop always behaves as a magnetic dipole. Atoms with completely filled shells have zero magnetic moment because the orbital and spin magnetic moments cancel each other.

Answer 1

The Correct Option is D

To determine the validity of the assertion and reason, we need to understand the concepts of magnetic moments in atoms and the behavior of current loops as magnetic dipoles.

1. Assertion (A): All atoms have a net magnetic moment.
   • Atoms consist of electrons that have intrinsic magnetic moments due to their spin and orbital angular momenta. However, the net magnetic moment of an atom depends on the arrangement and pairing of these electrons.
   • In many atoms, especially those in filled electron shells, the magnetic moments of electrons pair up and cancel out, resulting in no net magnetic moment.
   • Therefore, it is incorrect to say that all atoms have a net magnetic moment. The assertion is false.
2. Reason (R): A current loop does not always behave as a magnetic dipole.
   • A current loop can be modeled as a magnetic dipole, as it generates a magnetic field similar to a bar magnet. The magnetic dipole moment (\mu) of a current loop is given by the product of current (I) and the area (A) of the loop, with its direction determined by the right-hand rule.
   • A current loop always behaves as a magnetic dipole, regardless of its orientation or the external fields applied to it. The reason is false.

Both the assertion and the reason are false. The correct answer is: Both Assertion (A) and Reason (R) are false.