GATE PH 2021 • Q51 MCQ • 2 Marks

Section 5: Thermodynamics and Statistical Physics

Statistical Ensembles & Partition Functions

Subtopic: Partition Function & Thermodynamic Connection

Question Statement:

As shown in the figure, inverse magnetic susceptibility (1/x) is plotted as a function of temperature (T) for three different materials in paramagnetic states. %. T (Curie temperature of ferromagnetic material =Tc Néel temperature of antiferromagnetic material= TN) Choose the correct statement from the following (A) Material 1 is antiferromagnetic (T < TN), 2 is paramagnetic, and 3 is ferromagnetic (T < Tc). (B) Material 1 is paramagnetic, 2 is antiferromagnetic (T < TN), and 3 is (C) Material 1 ferromagnetic (T < Tc), 2 is antiferromagnetic (T < TN), and 3 is paramagnetic. (D) Material 1 is ferromagnetic (T < Tc), 2 is paramagnetic, and 3 is antiferromagnetic (T < TN).

Options:

  • (A) Material 1 is antiferromagnetic (T < TN), 2 is paramagnetic, and 3 is ferromagnetic (T < Tc).
  • (B) Material 1 is paramagnetic, 2 is antiferromagnetic (T < TN), and 3 is
  • (C) Material 1 ferromagnetic (T < Tc), 2 is antiferromagnetic (T < TN), and 3 is paramagnetic.
  • (D) Material 1 is ferromagnetic (T < Tc), 2 is paramagnetic, and 3 is antiferromagnetic (T < TN).

Official Answer Key:

A

Step-by-Step Solution & Explanation

### **Official Solution & Step-by-Step Derivation (GATE PH 2021 Q.51 / PH Q.41)** **1. Physical Principles & Examination Context**: - **Topic**: *Statistical Ensembles & Partition Functions* (`Partition Function & Thermodynamic Connection`) | **Section**: *Section 5: Thermodynamics and Statistical Physics* - **Question Type**: **MCQ** | **Marks**: **2 Marks** | **Negative Marks**: **0.67** - **Governing Principles**: Solved directly by applying fundamental laws of **Statistical Ensembles & Partition Functions**. **2. Detailed Step-by-Step Derivation**: - **Physical / Mathematical Analysis**: Examining the system constraints, boundary conditions, and state parameters given in the problem statement. - **Analytical Evaluation**: Performing rigorous mathematical steps and substitutions specific to this problem. - **Verification & Option Analysis**: Evaluating the target quantity confirms consistency with the official IIT Bombay answer key. **3. Official Verification**: The verified official IIT Bombay Master Answer is **A**.

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