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# commutators question? Watch

1. Am I doing this correctly? thanks
2. (Original post by importunate)
Am I doing this correctly? thanks
I think you lost a minus sign in the first term for your [p, H] commutator. Since the question does state "for any potential V" you'd generally expect the commutator to depend on the form of V.

You also lost a minus sign in the second term for [p^2, T].

An easier way to do these questions is to note that [A, A^n] = 0 for any operator A so it's not always necessary to evaluate the commutator explicitly unless the question says to.
3. however i do it, a comes out to be zero... and not in terms of the potential. what do you get it to be?
4. (Original post by importunate)
however i do it, a comes out to be zero... and not in terms of the potential. what do you get it to be?
You have to use the product rule. The d/dx acts on V*psi not just psi since V=V(x)
5. Ok using the product rule I get: -i(hbar)dv/dx

Is that correct?
6. (Original post by importunate)
Ok using the product rule I get: -i(hbar)dv/dx

Is that correct?
That looks right from memory.

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