Semicircular potential well

In quantum mechanics, the case of a particle in a one-dimensional ring is similar to the particle in a box. The particle follows the path of a semicircle from 0 {\displaystyle 0} to π {\displaystyle \pi } where it cannot escape, because the potential from π {\displaystyle \pi } to 2 π {\displaystyle 2\pi } is infinite.