Question Bank MCQ • 1 Mark Section 4: Quantum Mechanics Perturbation theory

QB_PH_106: Perturbation theory

Question Statement

The Rayleigh-Ritz variational expectation $\langle \psi_{trial} | H | \psi_{trial} \rangle$ for normalized $\psi_{trial}$ is always:
(A) \ge E_0 \text{ (upper bound to true ground state energy)}
(B) \le E_0
(C) = E_0
(D) \text{Unbounded}
Correct Answer
A
Verified Key

Step-by-Step KaTeX Derivation & Detailed Explanation

### Solution: The variational energy always provides a rigorous upper bound to the ground state energy.
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