All physics students ought to know about the photoelectric effect. In fact, heck, all people should know about the photoelectric effect. It's incredibly important to our world.
Here's a short summary. Scientists discovered that many metals actually release electrons when light is shone upon them. Some thought that this meant that the light was simply accelerating or energizing the electrons until they jumped out of the metal. However, upon further testing and changing of the intensity of the light, this was proven untrue. This is incredibly important because it means that light is actually made up of little particles called photons that are striking the electrons in the metal and knocking them out. This idea forms half of the basis for the wave-particle duality of light which has opened up so many quantum mechanics questions.
So, we know that. But, do you know how we use this effect today? Let's see!
Night vision goggles use this technology. Photons hitting the goggles strike a metal screen, emitting electrons which then can be accelerated by an electric field. They are then sent to a phosphorous screen where their increased speed shows up brightly. Thus, weak light and radiation outside the visible spectrum can be enhanced to be used for seeing in the dark. This process is used for photomultipliers, though they don't emit any radiation initially.
The original video capturing devices used it to dissect images. Light hits the photocathode inside the device, sending electrons which are detected and whittled down to only the desired section of the image, which is then deflected to a display device like a cathode ray tube to be viewed.
These following aren't uses, but they're still cool! The dust on the moon is actually electrically charged by the sun's light, and levitates above the surface. Spacecrafts facing the sun develop unbalanced charges from its light, which can threaten delicate instruments. Electroscopes can't be used to test for static electricity if exposed to too intense light.
In the end, the photoelectric effect is a really cool way to transform light data into electrical, which can then be controlled magnetically as well, opening up the possibilities for the study and usage of light. How cool is that!