Millikan proved validity of Einstein’s photoelectric equation by

Millikan made series of experiments and obtained slope of V₀ → v graph i.e. $\frac{\mathrm{h}}{\mathrm{e}}$. He obtained value of slope. Using the value of slope and charge of electron, he obtained value of Planck's constant i.e. h = 6.626×10⁻³⁴ J-s which was known value. Millikan made experiment on number of alkali metals for large range of incident radiation and verified photoelectric equation with great precision.