The double slit experiment: the experiment that tried to see if light is a particle or a wave. Once through two slits in the barrier, light showed bands of dark and light, indicating that there was a pattern of interference.
This is similar to what happened with waves, with zones of constructive and destructive interferences of waves from each slit.
1.2 Photoelectric Effect
The Experiment:
“Lenard’s experiments involved beams of light of a single color (monochromatic light) which means that all the waves in the light have the same frequency. Using a brighter light (he actually moved the same light closer to the metal surface, which has the same effect) there is more energy shining on each square centimeter of the metal surface. If an electron gets more energy, then it ought to be knocked out of the metal more rapidly, and fly off with a greater velocity. But Lenard found that as long as the wavelength of the light stayed the same all of the ejected electrons flew off with the same velocity. Moving the light closer to the metal increased the number of electrons that were ejected, but each of those electrons still came out with the same velocity as the ones produced by a weaker beam of light of the same color. On the other hand, the electrons did move faster when he used a beam of light with a higher frequency—ultraviolet, say, instead of blue or red light.”