Analysis of a sudden doubling of the space between walls of an infinite 1-dim square well: a surprising result at first

Abstract In this work, we would like to point out how an usually recommended exercise in Quantum Mechanics textbooks can lead to a surprising result at first, and how the clarification of this surprising result can help to reinforce ideas of Quantum Mechanics. We consider the problem of a particle in an infinite square well which suddenly has its width doubled. The surprise arrives in the fact that different results can be obtained whether the well is considered non-symmetrical or symmetrical, even though both are physically identical, as it is well-known.