Estimation of the experimental error of a single measurement. Error propagation. Least square fitting. Non-elastic electron scattering (Frank – Hertz experiment). Photoelectric effect (experimental estimation of the Planck’s constant). Wave nature of the electrons (electron diffraction). Experimental estimation of the e/m ratio of electrons. Thermionic emission (Richardson formula). A study of the energy quantum levels of Na atoms via the observation of atomic spectra as well as observation of their fine structure.