* Einstein's theory: In 1905, Einstein proposed that light exists as quantized packets of energy called photons. He explained the photoelectric effect by suggesting that a photon's energy is transferred to an electron in a metal, causing the electron to be emitted.
* Millikan's experiments: Millikan's experiments, conducted between 1912 and 1916, were designed to disprove Einstein's theory. He meticulously measured the energy of emitted electrons as a function of the frequency of light shining on a metal surface. His results showed that the energy of the emitted electrons was directly proportional to the frequency of light, with a constant of proportionality being Planck's constant, exactly as Einstein had predicted.
* The significance: Millikan initially aimed to disprove Einstein's idea, but the precision of his experiments ended up providing some of the most compelling evidence for the existence of photons and the validity of Einstein's theory.
In summary: Millikan's experiments, designed to disprove Einstein, actually confirmed Einstein's theory of the photoelectric effect and solidified the concept of light quanta, or photons.
