Hi, i am beginning elementary Quantum Mechanics as my course. While studying one question arise in my mind : In the solution of Schrodinger wave equation there are two parts. ψ=A*exp(jKx) + B*exp(-jkx). (for confined electron) But when dealing with free electron the solution is of the following pattern : ψ = A*exp(jkx) or ψ = B*exp(-jkx). Can any one tell me the reason behind that?