# Quantum Mechanics; Expectation value

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1. May 5, 2017

### Stephen_G

1. The problem statement, all variables and given/known data
At t=0, the system is in the state . What is the expectation value of the energy at t=0?

I'm not sure if this is straight forward scalar multiplication, surprised if it was, but we didn't cover this in class really, just glossed through it. If someone could walk me through this, it would be most appreciated.
2. Relevant equations

3. The attempt at a solution
I just multiplied the 1/sqrt2 by 1 and i. I'm certain that this is not the correct.

2. May 5, 2017

### Staff: Mentor

How, and why?

You need to know the energies of the two states, at least as variables.

If you measure which state the particle is in, what are the possible results? What is the energy associated with each result? What is the probability?

3. May 5, 2017

### Stephen_G

Would the energies be the eigenvalues? I got those in the first portion of that question.

The first question asked for the eigenvlaues and vectors for the hamiltonian:

4. May 5, 2017

### Staff: Mentor

Please post the full question with all relevant context, otherwise there is too much guesswork involved.

In general, how do you find the expectation value of an operator?

5. May 5, 2017

### Stephen_G

Sorry about that, I will in the future.
But, for the your question, you would just insert your expectation value into your braket <Ψ|A|Ψ> and solve, correct?

6. May 6, 2017

### Staff: Mentor

That works, sure.