You are studying the absorption of electromagnetic radiation by electrons in a crystal structure. The situation is well described by an electron in a cubical box of side length L.The electron is initially in the ground state. You observe that the longest-wavelength photon that is absorbed has a wavelength in air of l = 624 nm. What is L?

You are studying the absorption of electromagnetic radiation by electrons in a crystal structure. The situation is well described by an electron in a cubical box of side length L.The electron is initially in the ground state. You observe that the longest-wavelength photon that is absorbed has a wavelength in air of l = 624 nm. What is L?