Six Electrons Are in a Two-Dimensional Square Potential Energy Well

Multiple Choice

Six electrons are in a two-dimensional square potential energy well with sides of length L. The potential energy is infinite at the sides and zero inside. The single-particle energies are given by where n_x and n_y are integers. If a seventh electron is added to the system when it is in its ground state the least energy the additional electron can have is:

A) 2(h²/8mL²)
B) 5(h²/8mL²)
C) 10(h²/8mL²)
D) 13(h²/8mL²)
E) 18(h²/8mL²)