A few quick questions I'd like cleared up: 1) Alkali metals are said to have a really low threshold energy, enough for visible light to cause the photoelectric effect. Does this mean if I aim a flashlight (turned on) at a piece of sodium, I could ionise it? Simply flashing a light over a piece of alkali metal could give it a positive charge? Surely they'd always be positively charged then? 2) It doesn't have to be IR-UV radiation does it? Not an 'actual colour' all the time, right? X-rays and gamma rays are more capable of the photoelectric effect, correct? 3) An electron dropping back to its ground state after excitation releases a photon of equal energy to the energy level difference (energy it gained from another electron or photon). Why is it I commonly read when waves are absorbed, they are re-emitted at a longer wavelength (therefore lower frequency)? E.g: Greenhouse effect. 4) When we see an absorption spectrum, can the photons only be absorbed by gases or do the black lines also account for photons absorbed by liquids/solids also in the way? 5) How can an electron emit more than one photon when relaxing? 6) In fluorescent tubes, do the electrons release UV photons because of how high the energy from the incident electrons is? Much appreciated.