Liaht 0 0 Light
"X ray by Roentgen in 1895. Cathode rays by William Crookes in 1879 Electrons by JJ Thomson. Mass of electrons 9.11 10A-31 Kg charge on electron is 1.602 * 10.19 c Photoelectric effect by Herta. Packets of energy called quantum or photons. Light is of dual nature.
The loosely bound electrons in the valence or outer most shell of the atoms are called free electrons. They cannot leave the surface. The free electrons are held inside the metal by attractive forces called restraining forces, causing potential barrier. WORK FUNCTION OF THE METAL-the minimum energy required by an electron to just escape from the metal surface so as to overcome restraining forces at the surface. Work function denoted by o and is measured in eV.