Auger Effect:
Auger observed that when x-ray beam is made to fall on a matter and it emits electrons from k-shell then vacancies are created in k-shells. These vacancies may be filled by electrons of l and m shells. If we consider that each photo-electron is followed by an x-ray photon, then number of photoelectron must be equal to number of x-ray photons but the number of photoelectrons emitted were more than number of x-ray photons. These extra emitted electrons are called Auger electrons and effect is called Auger effect.