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- 03-01-2011, 09:24 AMskycloud86Ask A Science Question
In this thread, users can ask a science question, and another user who knows the answer can help them out.

- 03-02-2011, 12:35 PMBote
What is a photon?

I need information that can not be found on wikipedia. Preferably some excerpts from genuine papers/experiments if you know of any. So far I've read Newton's and Einstein's theses and essays regarding light. Some other contributors would be appreciated. - 03-02-2011, 05:25 PMKilgore Trout
**"Under the photon theory of light, a photon is a discrete bundle (or quantum) of electromagnetic (or light) energy. Photons are always in motion and, in a vacuum, have a constant speed of light to all observers, at the vacuum speed of light (more commonly just called the speed of light) of c = 2.998 x 108 m/s."**

Source:

Photon - What is a photon?

"Waves and particles seem to be diametrically opposed concepts: a wave fills a region in space, while an electron or ion has a well-defined location. That, at least, was the view before the discoveries of the first half of the 20th century. Those discoveries suggested that on the atomic scale, the distinction became blurred: waves had some properties of particles, and vice versa.

To find how a light wave passes through a telescope, one calculates its motion as if it filled the entire focusing mirror. Yet when that same wave gives up its energy to one individual atom, it turns out that it acts like a particle. Regardless of whether a light beam is bright or dim, its energy is always transmitted in atom-sized amounts, "photons" whose energy depends only on wavelength.

Observations have shown that such duality also existed in the opposite direction. An electron should in principle have at any time a well-defined location and velocity, yet experiments that measure them give a blurred result. Quantum physics tells us that arbitrary precision in such observations cannot be attained, but that the motion may be described by a wave.

This may be a good place for introducing new quantities and notations. An electromagnetic wave of wavelength λ (lambda, small Greek L) covers a distance of c meters each second, where c is the velocity of light in space, close to 300,000,000 meters/second. Its frequency ν (nu, small Greek N)--the number of up-and-down oscillations per second--is also the number of wave crests in that distance, and is therefore obtained by dividing c with the wavelength:

ν = c/ λ

A basic quantum law then states that the energy E in joules of a photon of light of frequency ν is

E = hν

where h = 6.624 10-34joule-sec is "Planck's constant", a universal constant that is fundamental to all quantum theory. It was introduced in 1900 by Max Planck, when he tried to explain the "black body" distribution of wavelengths in the light emitted by a solid hot object. Incidentally, it was the above formula, published by Albert Einstein in 1905, that later earned him the Nobel prize, not (as many still believe) his theory of relativity."

Source:

(S-5) Waves and Photons

Photon Model of Light

As proposed by Einstein, light is composed of photons, a very small packets of energy. The reason that photons are able to travel at light speeds is due to the fact that they have no mass and therefore, Einstein's infamous equation - E=MC2 cannot be used. Another formula devised by Planck, is used to describe the relation between photon energy and frequency - Planck's Constant (h) - 6.63x10-34 Joule-Second.

Source:

Theory of Light

"The Question

(Submitted July 31, 1996)

Do photons have mass? Because the equations E=mc2, and E=hf, imply that m=hf/c2 . Is it so?

The Answer

No, photons do not have mass, but they do have momentum. The proper, general equation to use is E2 = m2c4 + p2c2 So in the case of a photon, m=0 so E = pc or p = E/c. On the other hand, for a particle with mass m at rest (i.e., p = 0), you get back the famous E = mc2.

This equation often enters theoretical work in X-ray and Gamma-ray astrophysics, for example in Compton scattering where photons are treated as particles colliding with electrons."

Source:

Mass of the Photon

http://www.youtube.com/watch?v=Q4IBaHXwIlA

http://www.youtube.com/watch?v=FjHJ7FmV0M4

**Feynman Diagrams:**

Theory: Feynman Diagrams (SLAC VVC) - 03-09-2011, 11:00 PMnameno1had
Can anyone help me with Hydrology Theory. I have a question that is tough to explain. If I could draw a picture and scan it and then diagram it I would.

This is my best try to help give you the proper mental image:

Imagine a tank filled with water. At the bottom of the tank there is a drain with a pipe that goes down and then turns 90 degrees and then once it reaches past the outer wall of the tank it again turns 90 degrees upward along side of the tank.After the pipe extends upward past the top of the tank it turns again 90 degrees until it reaches over the top of the tank.In essence if there was enough pressure the path of the pipe would allow water to flow out the drain and back into the top of the tank.

How much water would it take to weigh enough to cause enough pressure through a narrow enough pipe(so the weight of what is going up will be low enough) to get this flow achieved?

It seems possible in theory for perpetual motion, but I am not a hydrologist and I don't know all of the limitations.This is similar to what happens when a toilet is flushed or a sink is drained. The water has to travel through 2 -90 degree bends and one of them actually forces the water to flow up in order for it to flow back down.

If this was feasible you would think we would already do it. I would try to add a turbine for power, if it is possible. - 03-11-2011, 12:34 AMintjdude
- 03-11-2011, 12:55 AMnameno1had
- 03-11-2011, 12:58 AMMonkey Fritz
Nope. Sorry.

This is more of a fluid mechanics/fluid dynamics question.

If the system is closed, either it is full and the water remains stagnant, or the water from the overhead pipe would drain and be replaced by air.

Thnk of a bendy straw in a glass. Apply suction to the straw, then release the suction. The water drains back down the straw as pressure is equalized. The same effect would happen. Gravitiy's hold on the water is uniform, it doesn't matter how you channel it the force of gravity is the same, so the water equals out it's pressure.

The way I am saying doesn't even sound like it makes very much sense. This would be much easier to demonstrate than explain, but consider syphoning:

Siphon - Wikipedia, the free encyclopedia

You can use gravity to "pull" water up, but only if the end of the pipe is lower than your starting reservoir.

Actually, have you ever seen those plastic mugs with the straw built in to the handle? Same principle, the liquid pressure will always equal out. Doesn't matter how you design the base of the device, the pressure of the water will always be equal to the amount of water above. Consider fish tank design, the height of the tank is the only consideration in how thick the glass must be. If you have a three foot high tank that is only one foot by one foot and a three foot high tank that is ten feet by ten feet, the thickness of glass needed to support the pressure from the water is identical. - 03-11-2011, 01:03 AMnameno1had
that is cool because that means you could hypothetically put the pacific ocean in a tank that technically doesn't have a sealed bottom and it would still hold the water

I am sure there is a specific name for this principle, that is something else I specifically wanted to know - 03-11-2011, 01:05 AMMonkey Fritz
- 03-11-2011, 01:08 AMnameno1had
That makes some sense, the last time I checked there weren't any ocean feed geysers.

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