# Ehrenfest's Theorem

1. May 30, 2010

### 1Kris

If I had a hamiltonian of the form iA(p + c), where A is a constant matrix, p the momentum operator and c an ordinary constant how do I find the time rate of change of the expectation momentum value?
I've tried using Ehrenfest's theorem but I don't understand whether in [p,H], I should treat p as an operator or as an ordinary number? Could someone please make this clearer to me? Thanks.

2. May 31, 2010

### dextercioby

P is an operator in the commutator. Its commutator with itself is the zero operator.