An atom is capable of existing in two states a ground state of mass m and an excited state of mass m+a. if the transition from the ground by state to the excit

An atom is capable of existing in two states a ground state of mass M and an excited state of mass M+A. If the transition from the ground by state to the excited state proceeds by the absorption of a photon, the photon frequency in the laboratory frame (where the atom is initially at TFR-20091 rest) is