In this chapter, we shall investigate the interaction of a non-relativistic particle of mass and energy with various one-dimensional potentials, . Because we are searching for stationary solutions with unique energies, we can write the wavefunction in the form (see Section [sstat]) where satisfies the time-independent Schrödinger equation: In general, the solution, , to the previous equation must be finite, otherwise the probability density would become infinite (which is unphysical). Likewise, the solution must be continuous, otherwise the probability current ([eprobc]) would become infinite (which is also unphysical).