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

QB_PH_119: Perturbation theory

Question Statement

In degenerate perturbation theory, first-order energy shifts are determined by:
(A) Diagonalizing the perturbation matrix within the degenerate subspace
(B) Inverting the Hamiltonian
(C) Evaluating expectation in any state
(D) Summing off-diagonal terms
Correct Answer
A
Verified Key

Step-by-Step KaTeX Derivation & Detailed Explanation

### Solution: The roots of $\det(W - E^{(1)}I) = 0$ give the exact first-order energy splits.
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