A particle is in the quantum state ψ = n1Φ1 + n2Φ2, that is the superposition of 2 eigenfunctions of energy Φ1 and Φ2 with energy eigenvalues E1 and E2. What is the probability of measuring E2?

A particle is in the quantum state ψ = n1Φ1 + n2Φ2, that is the superposition of 2 eigenfunctions of energy Φ1 and Φ2 with energy eigenvalues E1 and E2. What is the probability of measuring E2? Correct Answer |n2|2

Since ψ is normalized, and Φ1 and Φ2 are orthogonal, |n1|2 + |n2|2 = 1. This means that the probability of measuring E2 is |n2|2 as the total probability must add to 1. Individual eigenstates are always orthogonal to each other.

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