Question:
Assertion (A) : All atoms have a net magnetic moment.
Reason (R) : A current loop does not always behave as a magnetic dipole.
Assertion (A) : All atoms have a net magnetic moment.
Reason (R) : A current loop does not always behave as a magnetic dipole.
Show 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.
Updated On: Jul 2, 2026
- Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
- Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
- Assertion (A) is true, but Reason (R) is false.
- Both Assertion (A) and Reason (R) are false.
Show Solution
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The Correct Option is D
Solution and Explanation
Concept:
The magnetic moment of an atom arises due to:
• Orbital motion of electrons around the nucleus.
• Spin motion of electrons. However, in many atoms, the magnetic moments of electrons pair up and cancel each other. Therefore, not every atom possesses a net magnetic moment. Furthermore, a current-carrying loop always behaves as a magnetic dipole and possesses a magnetic dipole moment given by \[ \vec{\mu}=IA\hat{n}, \] where \(I\) is the current in the loop and \(A\) is its area.
Step 1: Examine the Assertion (A).
The statement says: \[ \text{All atoms have a net magnetic moment.} \] This is incorrect because atoms having completely filled electronic shells have zero resultant magnetic moment due to cancellation of individual electron moments. For example: \[ \text{He, Ne, Ar} \] have zero net magnetic moment. Hence, Assertion (A) is false.
Step 2: Examine the Reason (R).
The statement says: \[ \text{A current loop does not always behave as a magnetic dipole.} \] This is also incorrect because every current loop behaves like a magnetic dipole and has a definite magnetic dipole moment. Hence, Reason (R) is also false. Therefore, \[ \boxed{\text{Both Assertion (A) and Reason (R) are false.}} \]
• Orbital motion of electrons around the nucleus.
• Spin motion of electrons. However, in many atoms, the magnetic moments of electrons pair up and cancel each other. Therefore, not every atom possesses a net magnetic moment. Furthermore, a current-carrying loop always behaves as a magnetic dipole and possesses a magnetic dipole moment given by \[ \vec{\mu}=IA\hat{n}, \] where \(I\) is the current in the loop and \(A\) is its area.
Step 1: Examine the Assertion (A).
The statement says: \[ \text{All atoms have a net magnetic moment.} \] This is incorrect because atoms having completely filled electronic shells have zero resultant magnetic moment due to cancellation of individual electron moments. For example: \[ \text{He, Ne, Ar} \] have zero net magnetic moment. Hence, Assertion (A) is false.
Step 2: Examine the Reason (R).
The statement says: \[ \text{A current loop does not always behave as a magnetic dipole.} \] This is also incorrect because every current loop behaves like a magnetic dipole and has a definite magnetic dipole moment. Hence, Reason (R) is also false. Therefore, \[ \boxed{\text{Both Assertion (A) and Reason (R) are false.}} \]
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