How Do Solar Panels Work?

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They’re an increasingly common sight on the tops of buildings and residential properties: sometimes blindingly reflective panels that absorb sunlight and convert it into usable energy. Noted futurist Ray Kurzweil thinks we’ll all be using them by 2028. But how do solar panels work? Your basic understanding of solar panels—that they convert sunlight directly into electricity—is true. It’s called the photoelectric effect, and it was first discovered in the 1800s. Scientists learned that photovoltaic (PV) cells made of selenium were ideal for this purpose. While they later turned to the semi-conductor silicon, the idea remained the same: Up to a third of the energy found in the sun’s rays could, theoretically, be harnessed for electrical power under the most basic setup, and over 40 percent for the more expensive and complicated models. Silicon crystals by themselves aren’t necessarily great for this purpose, though. They need to be altered with boron and phosphorus and layered. The layer of boron-altered silicon has fewer electrons than it needs to form a bond, so an electron “hole” is created. The layer of phosphorus-altered silicon, meanwhile, has too many electrons. The space between is known as the P-N junction. As the sun’s photons enters the PV cells and starts dislodging electrons, the charge attempting to travel through the P-N junction gets diverted to an external circuit that can then carry the power to an inverter. You may not realize that the power generated with this method is a direct current, or DC, the same type found in batteries. To use the energy in a home or building, it needs to be converted to AC, or alternating current, the type found in outlets. And this is the role of the inverter. This kind of green energy has numerous benefits. Electricity doesn’t need to be transported by a utility company to the premises, and excess can be returned right back to the grid. If you’re thinking of installing a system, however, there are some caveats. For one, the upfront cost can be significant—around $10,000 to $13,475, depending on where you live, after tax credits. While you may be able to cut those costs with state rebate incentives or financing, it may take some time to recoup that investment. On the other hand, once installed, solar panels don’t appear to require much maintenance. Without moving parts, they’re not likely to suffer from mechanical issues, although you may need to replace the inverter at some point, which can get expensive. A site like EnergySage.com can also use your specific location to calculate how much a solar panel system might save you. So how do solar panels work? It’s one part the photoelectric effect and one part economy. If Kurzweil is correct, it won’t be long before we’ll all be well-versed in both benefits. Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

What's the Difference Between Pigeons and Doves?

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To the layman, the difference between pigeons and doves has something to with color, maybe. Or location. Or general appeal (doves usually get much better press than pigeons do). But what’s the actual, scientific difference between doves and pigeons?

As it turns out, there isn’t one. Paul Sweet, the collection manager for the department of ornithology at the American Museum of Natural History, says the difference is more linguistic than taxonomic.

“The word dove is a word that came into English from the more Nordic languages, whereas pigeon came into English from French,” Sweet tells Mental Floss.

Both dove and pigeon refer to the 308 species of birds from the Columbidae family, Sweet says. There’s no difference between a pigeon and a dove in scientific nomenclature, but colloquial English tends to categorize them by size. Something called a dove is generally smaller than something called a pigeon, but that’s not always the case. A common pigeon, for example, is called both a rock dove and a rock pigeon.

“People just have their own classification for what makes them different,” Sweet says. “So in the Pacific, for example, the big ones might get called pigeons and the smaller ones might be called doves, but they’re actually more closely related to each other than they are to other things in, say, South America, that are called pigeons and doves.”

The difference boils down to linguistic traditions, so feel free to tell people you’re releasing pigeons at your wedding or that you’re feeding doves in the park. Scientifically speaking, you’ll be correct either way.

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What Is the Wilhelm Scream?

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What do Star Wars, The Lord of the Rings, Pirates of the Caribbean, Harold and Kumar Go to White Castle, Toy Story, Reservoir Dogs, Titanic, Anchorman, 22 Jump Street, and more than 200 other films and TV shows have in common? Not much besides the one and only Wilhelm Scream.

The Wilhelm Scream is the holy grail of movie geek sound effects—a throwaway sound bite with inauspicious beginnings that was turned into the best movie in-joke ever when it was revived in the 1970s.

Just what is it? Chances are you’ve heard it before but never really noticed it. The Wilhelm Scream is a stock sound effect that has been used in both the biggest blockbusters and the lowest low-budget movies and television shows for over 60 years, and is usually heard when someone onscreen is shot or falls from a great height.

First used in the 1951 Gary Cooper western Distant Drums, the distinctive yelp began in a scene in which a group of soldiers wade through a swamp, and one of them lets out a piercing scream as an alligator drags him underwater.

As is the case with many movie sound effects, the scream was recorded later in a sound booth with the simple direction to make it sound like “a man getting bit by an alligator, and he screams.” Six screams were performed in one take, and the fifth scream on the recording became the iconic Wilhelm (the others were used for additional screams in other parts of the movie).

Following its debut in 1951, the effect became a regular part of the Warner Bros. sound library and was continually used by the studio’s filmmakers in their movies. Eventually, in the early 1970s, a group of budding sound designers at USC’s film school—including future Academy Award-winning sound designer Ben Burtt—recognized that the unique scream kept popping up in numerous films they were watching. They nicknamed it the “Wilhelm Scream” after a character in the first movie they all recognized it from, a 1963 western called The Charge at Feather River, in which a character named Private Wilhelm lets out the pained scream after being shot in the leg by an arrow.

As a joke, the students began slipping the effect into the student films they were working on at the time. After he graduated, Burtt was tapped by fellow USC alum George Lucas to do the sound design on a little film he was making called Star Wars. As a nod to his friends, Burtt put the original sound effect from the Warner Bros. library into the movie, most noticeably when a Stormtrooper is shot by Luke Skywalker and falls into a chasm on the Death Star. Burtt would go on to use the Wilhelm Scream in various scenes in every Star Wars and Indiana Jones movie, causing fans and filmmakers to take notice.

Directors like Peter Jackson and Quentin Tarantino, as well as countless other sound designers, sought out the sound and put it in their movies as a humorous nod to Burtt. They wanted to be in on the joke too, and the Wilhelm Scream began showing up everywhere, making it an unofficial badge of honor. It's become bigger than just a sound effect, and the name “Wilhelm Scream” has been used for everything from a band name, to a beer, to a song title, and more.

But whose voice does the scream itself belong to? Burtt himself did copious amounts of research, as the identity of the screamer was unknown for decades. He eventually found a Warner Bros. call sheet from Distant Drums that listed actors who were scheduled to record additional dialogue after the film was completed. One of the names, and the most likely candidate as the Wilhelm screamer, was an actor and musician named Sheb Wooley, who appeared in classics like High Noon, Giant, and the TV show Rawhide. You may also know him as the musician who sang the popular 1958 novelty song “Purple People Eater.”

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