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The cutoff frequency is basically the minimum frequency that is required to start the emission of electrons. Below the cutoff frequency the phenomenon of photoelectric effect stops altogether. When a light ray/wave/electromagnetic radiation falls on a metallic surface,having a frequency≥threshold frequency,a part of the energy of the incident radiation(known as threshold work function) gets absorbed by the electrons on the metallic surface;this absorbed energy facilitates electronic excitement.The remaining portion (i.e, energy of incident radiation-threshold work function)gets transformed into the kinetic energy of the electrons and accounts for their ejection.