An electron is trapped in a 1-dimensional box that is 401 nm wide. Initially, it is in the n = 4 energy level, but after a photon is absorbed the electron is in the n = 7 energy level. What was the wavelength of the absorbed photon?
Eventually, the electron ends up in the ground state. As it does so, one or more photons are emitted during those transitions. Find the wavelengths of the least energetic and most energetic photons that might be emitted during the all the possible transitions to the ground state.