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Author Topic: Ask your dumb Science questions here, you idiot  (Read 34022 times)
Metsfan
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« Reply #40 on: July 03, 2013, 02:26 pm »

That's some really cool stuff to look into. Thanks guys
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thermus aquaticus
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« Reply #41 on: July 04, 2013, 11:42 pm »

It's actually rather hot.
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HyperGlavin
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« Reply #42 on: July 05, 2013, 02:07 am »

And don't look into it. Smoke inhalation is a serious matter.
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ThomasLuna
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« Reply #43 on: August 14, 2013, 12:58 am »

LEDs and solar panels required understanding of quantum to make. They both work essentially as being 2 different types of semiconductor in contact with each other in a circuit though, so YaoMing covered it, essentially.

Semiconductors can be doped with impurities that have an excess of electrons or impurities with a deficit of electrons, either type of impurity can allow them to conduct, but the way they do it is slightly different.

A LED works because you have electrons going from a semiconductor with a high energy level molecular orbital to one with a lower energy level molecular orbital. When it makes the jump, that excess energy gets spit out as a photon of the difference in energy between the two molecular orbitals.

A solar panel works because you have electrons going from a semiconductor with a low energy level molecular orbital to one with a higher energy level molecular orbital. When the electron hits the barrier between these two, it is stuck and needs more energy to jump to the new semiconductor, but along comes light of the right amount of energy, and the electron can pop across and continue its merry way, having gained energy equivalent to how much that photon had.
Ya nice information on leds and solar panels.. These two technologies are mostly used worldwide as they are very energy efficient..
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ThomasLuna
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« Reply #44 on: August 14, 2013, 01:18 pm »

led lights and solar panels required understanding of quantum to make. They both work essentially as being 2 different types of semiconductor in contact with each other in a circuit though, so YaoMing covered it, essentially.

Semiconductors can be doped with impurities that have an excess of electrons or impurities with a deficit of electrons, either type of impurity can allow them to conduct, but the way they do it is slightly different.

A LED works because you have electrons going from a semiconductor with a high energy level molecular orbital to one with a lower energy level molecular orbital. When it makes the jump, that excess energy gets spit out as a photon of the difference in energy between the two molecular orbitals.

A solar panel works because you have electrons going from a semiconductor with a low energy level molecular orbital to one with a higher energy level molecular orbital. When the electron hits the barrier between these two, it is stuck and needs more energy to jump to the new semiconductor, but along comes light of the right amount of energy, and the electron can pop across and continue its merry way, having gained energy equivalent to how much that photon had.

Ya nice information on leds and solar panels.. These two technologies are mostly used worldwide as they are very energy efficient..
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barco
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« Reply #45 on: August 14, 2013, 01:38 pm »

Dudes, what the fuck is fire. What is it. Is it like an energy or a plasma or hot stuff emitting photons or what. What is it.
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pingollum
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« Reply #46 on: August 14, 2013, 01:57 pm »

silly barco, fire is the second of the four elements everyone know this
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pingollum
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« Reply #47 on: August 14, 2013, 01:59 pm »

the fifth element is led lights

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Johnny Roastbeef
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« Reply #48 on: August 14, 2013, 03:31 pm »

Whoo, I'm all up in this one. 

What you're used to calling fire is basically just hot gases.  Orange flames like a candle or a campfire are made up of radiating particles. Macroscopic particles like soot radiate in the broadband like black bodies (though more technically are gray bodies).  So what you're seeing as the flame is many tiny particles glowing hot just like iron or steel heated til orange.   

More carefully controlled flames, like a natural gas flame that glows blue, typically have that color as the result of purely molecular photon emission.  For example, when OH radicals, present in all hydrocarbon combustion, go through one of the many steps in their reaction chain, photos are emitted in the UV around 308nm. The blue color we see in those flames comes from a combination of excited co2 radicals, and from excited CH radicals.  These are found in all hydrocarbon reaction mechanisms and is part of why methane, propane, etc flames can look similar at a glance. This type of emission is called chemiluminescence.

This emission occurs in the spatial region where chemical reactions are actually occurring, and in fact, we use filtered pictures of only those colors to detect exactly where the flame is.  Many flames though can also produce visible emission even in the post flame region, if enough hot gas is present in an ionized state.  This is somewhat common with impurities or trace chemicals.  Lastly, even nice gaseous flames like this can produce soot and glow orange.  It's especially common in hydrocarbon fuels that have a double or triple bond, because those promote the formation of ring-structure hydrocarbons which are precursors to soot, which is basically just pure carbon.  So something like acetylene or ethylene, when burning rich, or in a non premixed mode, will often have a bright orange-yellow region, almost like in a candle flame, where black body emission from soot particles outshines the chemical emission.

Some flames, notably hydrogen, produce no visible flame.  The team working on a hydrogen fuel cell vehicle at Virginia tech used to keep a broom handy to wave over the engine if they suspected a fire, because the flames weren't easily detectable otherwise, though would have been if they could see in the UV. 
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Johnny Roastbeef
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« Reply #49 on: August 14, 2013, 03:48 pm »

Here's a really good illustration in a laminar, premixed flame.



Note that the OH*, CH*, CO2* and C2* are always present in all these flames, but are present in varying amounts that cause the color and appearance to change.  The *'s denote that the species is present in an excited state.  The figure with CO2* labelled is an example of kind of "post-flame-but-still-excited-gas" stuff. 

The thin sheets visible on the edges of the phi=0.7 flame are basically the region where reactions occur.  The luminescence you see in between those is there because the cone is 3-D.  If you took a cross sectional slice, you would see a triangle of flame/reaction zone, with nothing in the middle (cold unburnt reactants that haven't reacted yet) and nothing outside (hot burnt products that are done reacting). 
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Karlski
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« Reply #50 on: August 14, 2013, 05:38 pm »

That was cool and informative, JRB, and I didn't even ask the question!
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Remington Lonespear
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« Reply #51 on: August 14, 2013, 06:23 pm »

So, magic. Got it.
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« Reply #52 on: August 14, 2013, 06:38 pm »

That was heck of rad. Thanks JRB!
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« Reply #53 on: August 14, 2013, 07:31 pm »

That was a softball, since that's what my dissertation was on.  I actually had to stop myself from writing more.
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barco
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« Reply #54 on: August 15, 2013, 09:58 am »

Word, thanks JRB.
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norumaru
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« Reply #55 on: October 03, 2013, 12:53 pm »

What is the difference between direct and alternating current? I understand the technological difference, but what are the consequences for the user and why?
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« Reply #56 on: October 03, 2013, 03:11 pm »

It all has to do with back-end stuff, electrical transmission. If what came through the mains were DC instead of AC, your appliances would all be built to work that way. The issue comes in converting AC to DC and back and the voltages at which it's easy to get the currents to.

First is transmission, the longer distance you send electricity, the more resistance losses there are on the way. The amount of resistance is

resistance = Power/(current^2)

The amount of power you are transmitting is:

Power=current * voltage

What matters to the consumer is how much power they are getting, so if that's essentially constant in any practical situation, you can double the voltage, have half the current, and 1/4th the resistance in transmission.

It's super easy to raise AC to a higher voltage, you use a transformer, a box with two sets of electrical wire coils in it and no moving parts, and it multiplies the power by #coils in exit loop/# coils in entering loop. That means you can multiply the voltage by 20 or 30 or more very easily for transmission, then easily drop it again.

It's super difficult to change DC voltage, it requires a motor/generator set, you're powering a motor which is then providing power to a generator. It has moving parts, is more expensive to set up, has more power loss, requires more maintenance, etc. It's completely impractical in most situations.
http://en.wikipedia.org/wiki/War_of_Currents


There's one exception, if you're transferring a huge amount of power a long distance underwater, then high voltage DC is better because at the same voltage, dc loses less power from capacitance losses. Salt water can transmit electricity through it because it is salty and so has ions in it. Power travelling through underwater cables ends up creating a capacitor due to electromagnetic interactions with the ions in the water outside of the cable, and this effect is less with direct current than with alternating current. This means that for long-distance underwater transmission, it's more effective to accept the more expensive and lossy DC voltage changes at each end to not have the capacitance loss during transmission.
http://en.wikipedia.org/wiki/High-voltage_direct_current
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Johnny Roastbeef
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« Reply #57 on: October 03, 2013, 04:59 pm »

Technically, AC is also easier to produce in a generator, or to produce rotation from in a motor.  It's sort of the "natural" way for the rotating-magnetic-field-in-coils concept that motors and generators are based on to work.  DC motors have to work around that fact by using a commutator to change around the connections.

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thermus aquaticus
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« Reply #58 on: October 13, 2013, 06:01 am »

It's impossible to overstate how handy AC is. A capacitor (two close but non-touching plates) blocks lower-frequency AC. An inductor (coil of wire) blocks higher-frequency AC. This means that, by varying the capacitance and inductance in a circuit, you can choose which frequencies you let through. This is how you tune a radio.

DC is essential to information technology (including radios) because it makes transistors work. Transistors are great because they allow one current to control another current. This means that a circuit can, in principle, entirely control itself, with no human turning knobs or pushing buttons. The complexity of the machine is thus limited only by ingenuity of its creator and the amount of power they can provide. This is how we were able to create a technological civilization that no one human can understand the entirety of, that will eventually slaughter us all and colonize the galaxy. The DC acts as a constant power source, enabling the transistor to amplify the signal current, or act as a switch in digital circuits.

Customarily, in a circuit diagram, the DC power path runs from top to bottom, while the signal path runs from left to right.

                    POWER
                       (+)
                        |
                        |
                          /\     /\
SIGNAL-->/ \ / \ /   \   /  \
                              \/     \
                        |
                        |
                       (-)

That's not what a circuit diagram looks like at all, but it does show the directions I described. Above was an analog AC signal. Below is a binary digital signal, which transcends our categories of AC and DC, and will some day transcend its creators.

                    POWER
                       (+)
                        |
                        |
SIGNAL-->....|||..||||...||
                        |
                        |
                       (-)
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CB
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« Reply #59 on: October 14, 2013, 03:18 am »

What the hell is string theory, and why is it so important so some people?
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