[5614]

What makes the difference (atomically and chemically) between a red substance and a blue substance?

I heard it was to do with the electron's osciallation (or frequency?) and it was to do with that and the oscillation (or frequency?) or the photon?

What i want to know is what makes some objects only emit (after absorbing) a photon of one frequency and not another?

[swansont]

It depends on the frequencies the material can absorb. Individual atoms have very distinct absorption bands, and when atoms form molecules and molecules form solids you have many different states, with ranges of frequencies, that can be absorbed.

But there are still frequencies that cannot be absorbed, or the probability is much smaller. These colors are reflected, while the others are absorbed.

[5614]

so it's all to do with what is absorbed and what isnt?

if so, what i was getting at is what makes certain atoms absorb x frequency and not y, and vice versa for another atom?

[blike]

Electron configuration.

[The Rebel]

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so it's all to do with what is absorbed and what isnt?

if so, what i was getting at is what makes certain atoms absorb x frequency and not y, and vice versa for another atom?

Would this delve into chemistry and the concepts of spectroanalysis (or whatever its called) along side energy levels.

I think it depends on the energy changes an electron has in the atom, and with different atoms having different makeups of electrons, so varies how the energies change when hit by a photon. By the photoelectric effect, when the atom changes its energy state, it emits a photon relative to this energy through E = hf.

[swansont]

The Rebel said:

I think it depends on the energy changes an electron has in the atom, and with different atoms having different makeups of electrons, so varies how the energies change when hit by a photon. By the photoelectric effect, when the atom changes its energy state, it emits a photon relative to this energy through E = hf.

That's not technically the photoelectric effect - you need to absorb a photon and ionize the atom for that. What you are describing is excitation and de-excitation.

[The Rebel]

swansont said:

That's not technically the photoelectric effect - you need to absorb a photon and ionize the atom for that. What you are describing is excitation and de-excitation.

A case of same girl different knickers surely?? :rolleyes:

Do I get 9/10 for effort.

Here's another question on colour though. How does the colour grey work? Is grey a weak energy level of pure white or is it a case of 50% of atoms absorbing photons and 50% atoms reflecting them.

[swansont]

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A case of same girl different knickers surely?? :rolleyes:

Do I get 9/10 for effort.

Here's another question on colour though. How does the colour grey work? Is grey a weak energy level of pure white or is it a case of 50% of atoms absorbing photons and 50% atoms reflecting them.

It's more a case of how high you're lifting her skirt :eek: :D

There are many colors that are not in the spectrum - grey, silver, gold, brown. These are a case of how we percieve things - many shades look different depending on the surrounding colors, and there are many optical illusions that take advantage of this.

[5614]

swansont said:

There are many colors that are not in the spectrum - grey, silver, gold, brown. These are a case of how we percieve things - many shades look different depending on the surrounding colors, and there are many optical illusions that take advantage of this.

i can see the answer to grey but what makes something look gold, silver or brown?

[swansont]

5614 said:

i can see the answer to grey but what makes something look gold, silver or brown?

As I said before, it's perception. Somwhere in the detection and processing of the information.

[5614]

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As I said before, it's perception. Somwhere in the detection and processing of the information.

that's not what i meant, but now i think i know the answer to what i meant!

like if you look at this image:



then you can clearly see black>grey>white so i know what makes something appear black, and i know what makes something appear white... but makes it appear grey?

its something to do with perception/detection/processing... but what to do with it? can you give more detail?

[J.C.MacSwell]

Isn't it just intensity?

[The Rebel]

J.C.MacSwell said:

Isn't it just intensity?

I've always struggle with grey even though it should be simple. What sort of electron makeup causes half of it to absorb photons and half of it to reflect them.

It's easy to produce grey on a screen just turn everything to half the intensity. But how come a material in what ever lighting is always grey until you can't see it (pitch black)

Here's a few more - what makes something "shiny" or "glossy"

Why does a piece of tin foil make the light that much brighter/intense than a plain mirror.

[YT2095]

Hmmm... having read all that, I`m left with the same answer I would have given to the OP.

much of it has to do with absorbtion and reflection of light after influence.

think of oil spread out on a pool of water, the oil is all the same molecule and yet you see all the colors of the rainbow from it, and they seem to "move" when you move, or a breeze from the wind creates a ripple effect.

in a Crystal, there can be no such influence, it is layer upon layer of perfection made solid.
it will remain one color :)

[swansont]

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think of oil spread out on a pool of water, the oil is all the same molecule and yet you see all the colors of the rainbow from it, and they seem to "move" when you move, or a breeze from the wind creates a ripple effect.

That's thin-film interference. Light reflecting from the top and bottom surface interferes. The thickness determines the wavlengths that will constructively and destructively interfere. It's most apparent when the layer is only a few wavelengths thick. Very spectacular when looking at acetone sprayed on a silicon wafer, since the acetone evaporates quickly and so the thickness changes rapidly.

[The Rebel]

YT2095 said:

much of it has to do with absorbtion and reflection of light after influence.

Could you please expand on that.