CBSE Class 12-science Answered

Work function of the metal is the minimum energy required just to get an electron out of its surface. Since electrons are present in a continuous band of levels, different electrons require different amounts of energy to get out of the atom.

Electrons which are least tightly held that is just at the surface of the metal, comes from the metal with maximum kinetic energy. However electrons below the surface are involved in collisions on their way out of the surface and, therefore emerge with energy which is less than the maximum value.

Hence, photoelectrons knocked off by a monochromatic radiation posses different energies.