What is in a beam of white light?

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What is in a beam of white light?
« on: 05/04/2011 06:30:03 »
Reuben asked the Naked Scientists:
Dear Chris,

So light is made up of photons, but in a light beam is there any other particles, like atoms, and if not what happened to the atoms that were there before the light beam?

And another...and another...and another.... what makes light go as fast as it does?

And is light mass-less?

And does light always go at the same speed, whether reflected off a mirror or in a vacuum like space?

Kind regards

What do you think?
« Last Edit: 05/04/2011 06:30:03 by _system »


Offline yor_on

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What is in a beam of white light?
« Reply #1 on: 05/04/2011 07:28:14 »
Light is massless.

Light meets atoms everywhere on earth, and if you consider it as 'photons' they interact and annihilate themselves with those atoms. The atom sends out a new photon as its gets excited by the new energy, that continue in the same direction until it meets a new atom that then etc, etc. As waves it interacts too but there we have the ideas of it getting reflected, scattered etc.

That's also why we have a blue sky, the atoms/molecules that gets excited absorbs the higher frequencies more readily than the lower, and blue is a high frequency, containing a lot of energy. The absorbed blue light is then radiated back, and scattered around in the atmosphere. And so the atmosphere becomes filled with a blue light at noon. When the evening comes you will see the opposite happening as the suns rays have to wander further in the atmosphere the lower the sun sets on the horizon, allowing only the lower spectrum to reach your eyes (red, yellow) with very little blue 'surviving'.

So what makes the colors is the way rays gets absorbed, reflected and scattered. Clouds that are white sends out a lot of scattered light, in all directions. If you take a strongly colored glass and crush it, into smithereens, you will find it become white as it now scatter the light everywhere instead of absorbing some frequency's and reflecting the other. the color you see when looking at a object is the frequency that it reflects. Dark material absorbs all frequency's and so becomes black.

Light always move at 'c'. It can be slowed by matter, and absorbed and remitted in form of a new photon but as soon it has 'space' around it it will be at 'c'. And you know what happens when it meets those atoms, right? And no, atoms are what makes molecules and matter so they have a size, but light, is just light. It's radiation, same as heat, having no size at all. It's strange :)
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Offline Geezer

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What is in a beam of white light?
« Reply #2 on: 05/04/2011 07:50:53 »
To appear white when it interacts with matter, the light has to be composed of photons with a range of different energy levels (electromagnetic frequencies) corresponding with the entire visible spectrum of light. If the light only consists of photons that fall within the red part of the spectrum for example, any matter illuminated by that light will appear to be red.

So "white light" is really a mixture of all possible colours of visible light.
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