GATE PH 2021 • Q30 NAT • 1 Mark

Section 7: Solid State Physics

Crystal Structure & Lattice Dynamics

Subtopic: Bragg's Law & X-ray Diffraction (Laue and Powder)

Question Statement:

A hoop of mass M and radius R rolls without slipping along a straight line on a horizontal surface as shown in the figure. A point mass m slides without friction along the inner surface of the hoop, performing small oscillations about the mean position. The number of degrees of freedom of the system (in integer) is M ////////

Official Answer Key:

2 to 2

Step-by-Step Solution & Explanation

### **Official Solution & Step-by-Step Derivation (GATE PH 2021 Q.30 / PH Q.20)** **1. Physical Principles & Examination Context**: - **Topic**: *Crystal Structure & Lattice Dynamics* (`Bragg's Law & X-ray Diffraction (Laue and Powder)`) | **Section**: *Section 7: Solid State Physics* - **Question Type**: **NAT** | **Marks**: **1 Mark** | **Negative Marks**: **0** - **Governing Principles**: Solved directly by applying fundamental laws of **Crystal Structure & Lattice Dynamics**. **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 **2 to 2**.

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