Scientific Seen

News, Commentary, and Tutorials from a Scientific Perspective

Nearly everything that uses electrical power has semiconductor circuits: your car, your coffeemaker, your computer. The performance of those circuits stems from the behavior of electrons within an ordered array of atoms, or a crystal lattice. Usually, the lattice is made from a base material of silicon atoms, with “dopants” added to increase or decrease the number of electrons in the material.

“N-type” semiconductor is made by introducing a dopant such as phosphorus, which brings extra electrons, whereas “p-type” has a dopant such as boron, which reduces the number of electrons compared to the base material. The interesting properties take place at the junction, where n- and p-type materials are brought into contact with one another. One of the things that happens is that the extra electrons from the n-type make their way to the p-side, and the missing electrons from the p-side, called “holes,” make their way to the n-side. The region in between is emptied of charge, hence the name “depletion region.”

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Originally published at eHow, SEP 2011

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Fusion reactions at the core of the sun power a circulating flow of incredible energies that culminate in the emission of tremendous amounts of electromagnetic radiation. The spectrum of the sun generally follows what’s known as a blackbody spectrum, which contains a certain amount of power across a spectral region stretching from ultraviolet to infrared. The form of the blackbody radiation makes it a relatively straightforward process to calculate the solar flux density that strikes Earth.

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Originally published at eHow, SEP 2011

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Projectile Motion Activities

Posted by rgaughan on 19 Sep 2011
Posted in eHow ArticlesTutorials  | Tagged With: | No Comments yet, please leave one

The entire universe works according to laws of physics, but in our ordinary experience so many different things are going on at once that it’s hard to figure out those rules. For example, every day we see objects fall, but it’s difficult to see the rules governing the motion of falling bodies. Galileo began the real understanding of projectile motion, and nowadays there are dozens of different demonstrations that help make visible the principles underlying projectile motion.

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Originally published at eHow, SEP 2011

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One of the reasons light is so useful is that, although it can do some pretty complicated things, it operates according to fairly straightforward rules. That might be hard to believe when you stand between two mirrors that face each other almost perfectly, and you can see a reflection of yourself going off into infinity, but that’s just a simple rule being applied over and over again with each reflection. Tri-fold mirrors operate by those same simple rules.

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Originally published at eHow, SEP 2011

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Imagine the fuel bill for the Space Shuttle. It’s hard enough to fill your car with 16 gallons of ordinary gas, so imagine the cost to fill a 526,000-gallon tank with rocket fuel. And that’s just to ferry a satellite into orbit. Once in orbit, satellites have to jet themselves around with fuel they’ve brought themselves. Space travel is expensive and there’s a constant search for less costly means of propulsion.

The thrust generated by a propulsion system is proportional to the mass of the propellant multiplied by its velocity. That is, a spacecraft sending 50 grams of propellant away at 3 meters per second has the same thrust as another sending 25 grams away at 6 meters per second. That’s the idea behind electric propulsion: Use less mass than traditional propulsion systems, yet expel it more rapidly. And bringing less mass into Earth’s orbit means the spacecraft is lighter, so it needs less expensive rocket fuel to the begin with.

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Originally published at eHow, SEP 2011

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