V ( r ) = V 0 {\displaystyle V(r)=V_{0}} (finite) for r < r 0 {\displaystyle r<r_{0}} and infinite elsewhere, or a particle in the spherical equivalent of the square well, useful to describe bound states in a nucleus or quantum dot. As the previous case, but with an infinitely high jump in the potential on the surface of the sphere. V(r) ~ r2 for the three-dimensional isotropic harmonic oscillator.