What happens to the observed frequency of a laser beam if it is approaching directly toward the observer at a high speed? What happens to its wavelength? Is it redshifted or blueshifted?
Draw a model of the hydrogen atom. Label the proton, electron, the ground state, and the first excited state.
What causes electrons to jump to excited states? What causes them to jump (or fall?) back down to lower energy excited states and ground states?
Draw a diagram which explains absorption and emission lines. Is it possible for the same gas cloud to have both absorption and emission lines. When can this happen? (Hint: think about Kirchoff's laws.)