what is the difference between absorption and emission spectrum
Absorption spectra is the spectrum found when the sample of the substance absorbs the radiation of a certain intensity and the electrons of the atoms jumps from lower energy level to higher.
while the emission spectra is obtained when the electron first jumps from lower to higher energy level and then further emits ir releases energy to attain the ground state. Then the spectrum obtained is emission spectrum.
Thus, emission spectra are produced by thin gases in which the atoms do not experience many collisions (because of the low density). The emission lines correspond to photons of discrete energies that are emitted when excited atomic states in the gas make transitions back to lower-lying levels.
n absorption spectrum occurs when light passes through a cold, dilute gas and atoms in the gas absorb at characteristic frequencies; since the re-emitted light is unlikely to be emitted in the same direction as the absorbed photon, this gives rise to dark lines (absence of light) in the spectrum.