we have a particle in an infinite one-dimensional square well potential [V(x)=0 for 0<x<L and V(x) is infinite otherwise] and introduce a small potential (perturbation) in the middle of the square well potential. Then the first order energy correction for the ground state is 100 times lower than the first order correction to the first excited state. I dont understand why... The wave function without the small potential step in the middle is zero in the middle for the first excited state and maximum in the middle for the ground state. Has the diffrence in energy corrections something to do with this?