![]() ![]() 1905 Albert Einstein explains the photoelectric effect.1902 Philipp Lenard observes that maximum photoelectron energies are independent of illuminating intensity but depend on frequency.1900 Max Planck states his quantum hypothesis and blackbody radiation law.1900 Johannes Rydberg refines the expression for observed hydrogen line wavelengths.1900 Paul Villard discovers gamma-rays while studying uranium decay.1896 Wilhelm Conrad Röntgen discovers the X-rays while studying electrons in plasma scattering X-rays-that were considered as 'waves' of high-energy electromagnetic radiation- Arthur Compton will be able to demonstrate in 1922 the 'particle' aspect of electromagnetic radiation.1887 Heinrich Rudolf Hertz discovers the photoelectric effect that will play a very important role in the development of the quantum theory with Einstein's explanation of this effect in terms of quanta of light.1898 William Ramsay and Morris Travers discover neon, and negatively charged beta particles.1898 Marie and Pierre Curie discovered the existence of the radioactive elements radium and polonium in their research of pitchblende.1897 Emil Wiechert, Walter Kaufmann and J.J.1896 Pieter Zeeman studies the splitting of sodium D lines when sodium is held in a flame between strong magnetic poles.1896 Antoine Henri Becquerel discovers the radioactivity of uranium.1895 William Ramsay discovers terrestrial helium by spectroscopically analyzing gas produced by decaying uranium.1894 Lord Rayleigh and William Ramsay discover argon by spectroscopically analyzing the gas left over after nitrogen and oxygen are removed from air.1887 Heinrich Hertz discovers the photoelectric effect.1885 Johann Balmer finds a mathematical expression for observed hydrogen line wavelengths.1873 Johannes van der Waals introduces the idea of weak attractive forces between molecules. ![]()
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