The amplitude for the absorption of a plane-polarized electromagnetic wave off a one- electron atom is proportional to1 here r is the electron position operator and p is the electron momentum operator. ip) and iv) are, respectively the initial and final electronic states. the vector k is in the directioin of the plane wave, and its magnitude k-. iki is the wave number. the angular frequency of the wave is ï-ck. îµ is the polarization of the electromagnetic wave. it is a unit vector perpendicular to k: á» . î­-1 and î­. k-0. the components of k and ofe are ordinary numbers, not operators.] let hh) be the 1s state of a hydrogen atom, and l) be the 2s state. suppose the wavelength of the radiation is long enough so that ka < 1, where a is the bohr radius. then if you compute the amplitude by expanding etkr, your answer will be a power series in ka. what is the first non-vanishing term in this expansion? [write this term as an integral, or sum of integrals, over hydrogen atom wave functions. don't take the time here to evaluate these integrals.]