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PaperBoy posted a blog entry in PaperLandAll 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!
TV's have risen in popularity tremendously since their invention, and despite continuing advancements in communication they continue to be a major project across the world. This relevance is in a large part due to the innovation which has kept them higher quality, easier to operate, and/or more useful than ever. TV's started out using cathode ray tube technology to display a picture. In this setup, a vacuum tube rockets electrons towards a phosphorescent screen. Anodes accelerate the electrons before they are deflected by two coils of electrically charged wire, creating an electric field. These deflected electrons strike the screen and glow in different colors due to the intensity with which the tube shoots them out. It scans left to right, top to bottom, until it finally reaches the bottom, and repeats. Nowadays, however, TV's work very differently. One style is the liquid crystal display. Lights on the bottom of the TV shine upwards, illuminating the inside of the TV. Two polarizing planes at 90 degree angles to each other block all regular light from reaching the screen. However, between the planes is a section of nematic liquid crystals which are twisted. On each end are glass planes coated with electrons to adjust intensity. As different voltages are applied to these glass panels, they twist and untwist the crystals in order to selectively block light from passing through the polarized plane to the screen. After the polarizing plane are one of three colorizing planes: red, green, or blue. By placing three of these arrangements next to one another, a pixel is created. Another style is the plasma display. In plasma displays, there are cells of ions and electrons free flowing, which are each pixels. Each pixel has a different color lens to transform visible light into one of the average three RBG. When an electric charge is sent to the cell, the positive ions and negative electrons both move around and combine with their opposites, creating light which passes through the colored panel and hits the screen. Whew! We need to stop making TV's and get back to books! Seriously, when's the last time someone reinvented the book? I want a plasma book.
We all know that atoms are comprised of electrons and a nucleus. The nucleus is tiny and dense with positive protons and neutral neutrons, while the electrons orbit far away and are negative. So then, why don't atoms fall through other atoms if there's so much empty space in between? Two reasons really: the electromagnetic repulsion and the Pauli exclusion principle. The first is simple. When you bring like charges together they repel, and this force is proportional to the inverse of the distance between the two charges squared. This means that if you bring objects closer and closer together, the resisting force will become greater and greater until it overcomes the force pushing the two objects together. The second theory could kill you if you aren't careful, so take breathers in the middle. Quantum mechanics dictates that electrons are in every possibility at once. So, really, there is no empty space between the electrons and the nucleus: it's all filled with possibilities. However, Pauli's exclusion principle also dictates that no two identical fermions (let's just say this includes electrons and move on) may occupy the same quantum state simultaneously. Thus, because both the electrons from one atom and the electrons from another atom cannot exist in the same place, but still fill up their surroundings with possibilities, at a certain point they become incredibly hard to push into each other any further. At this point you have what's called degenerate matter. Thus, crushing atoms into each other is almost impossible. The only reason we can pass through liquids and gasses is because we simply push them into the surrounding empty space or around each other.