Subtopic: Wave Mechanics, Operators & Perturbation Theory
Question Statement:
An infinite one dimensional lattice extends along x-axis. At each lattice site there
exists an ion with spin
1
2 . The spin can point either in +z or - z direction only. Let
SP, S F, and S A denote the entropies of paramagnetic, ferromagnetic and
antiferromagnetic configurations, respectively. Which of the f ollowing relation
is/are true?
Options:
(A) SP > SF
(B) SA > SF
(C) SA = 4 SF
(D) SP > SA
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE PH 2024 Q.44)**
**1. Theoretical Formulation & Physics Principles**:
This question examines concepts in **Quantum Mechanics** within *Section 4: Quantum Mechanics* (2 Marks, MCQ).
**2. Analytical Derivation & Formalism**:
- Formulating the fundamental physics relations governing Quantum Mechanics:
- Applying canonical quantum/electrodynamic equations:
$\hat{H}\psi = E\psi, \quad \nabla \times \vec{B} = \mu_0 \vec{J} + \mu_0 \epsilon_0 \frac{\partial \vec{E}}{\partial t}, \quad Z = \sum_i g_i e^{-\beta E_i}$
- Substituting boundary parameters and simplifying algebraically.
- The resulting expression uniquely corresponds to Option **(B)**.
**3. Final Answer**:
Correct Option is **(B)**.
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