John15 said:
I speak about the detail from personal experience, I can read a paper outside in bright sunlight go indoors and I need glasses, the only difference is the light intensity, if this was all down to focus paper would look the same whatever brightness of light.
Have been looking back through thread. A couple of things we talked about thermal radiation, post 27, anything with a temp above absolute 0 will emit EM radiation, of course in order to emit it has to absorb, wavelength also relates to temp so all things emit EM radiation in addition to any reflected light. All things that emit light are hot so all natural light must start as thermal radiation, ignoring chemical light.
Post 41 - 46 relate to photons energy of photon E=hf quote we don't talk about wavelength and photons together, frequency is dependant on wavelength so how do we separate wavelength and photons?
From what I have read it seems to me that quanta are waves with sufficient energy to react with electrons, as electrons have different energy levels the energy of the photon depends on the electron it interacts with.
Take the EM spectrum as a ramp then photons are steps in that ramp a specific places, they cause a form of phase transition in matter, they also join the world of infinite wavelengths with the finite world of matter, all other waves react indirectly as an increase in temp which reacts with all levels of matter.
I have been trying to find out about absorbtion spectra, specifically how much of the EM spectra is absorbed when all the lines are added together.
I have also been trying to find out how individual atoms react to waves that don't qualify as photons, do they just cause vibrations that are re-emitted as heat.
It has to be pointed out, from the start, that the whole business of reflection, scattering and the interaction of waves with solids is very complex. You won't get it until you have the basics all sorted out and understand what is meant by all the terms. You then need to get familiar with what happens when EM waves interact with single atoms. If you still have the time and energy, you can then move on to solids! (No such thing a s free lunch).
I suggest that you haven't actually read that but you are paraphrasing in an inaccurate way. Quanta are not waves and no one says they are. You could say that a photon is 'part of' a wave, in as far as that is the Quantum of the wave's energy that can be absorbed by a charge system. (No more and no less energy can be involved)
You can look upon a wave as a map, in space, of how the energy is being transported. The way the E and H fields vary in space and time follows the equation of the wave (the wiggly graph, if you like). That wave is the same, irrespective of the intensity / total energy flux.
This makes no sense at all. Waves don't "qualify as photons". Whenever there is an EM wave, there will be photons and they are all identical, it the wave just consists of one frequency (monochromatic). The only way that a wave can interact is via photons. When light hits a solid, you can get interactions with the system as a whole (in which case you are dealing with a system with large number of atoms which will have a concerted effect and this effect will be on the wave as a whole (a 'macroscopic effect, if you like). This will give you a reflection. If the surface is smooth, the resulting wave shape will be like that of the incident ray (wavefront) and you'll get a nice, specular reflection. If the surface is rough , there may be many reflections at different angles that will give a diffuse beam. A wave can also go through a solid without any great level of interaction. It can just get slowed down by the bulk effect. This accounts for refraction. Solids often absorb certain wavelengths, of course (glass tends to absorb IR and UV, for instance) but pass others. But impurities can be put into glass which will interact at the atomic level with certain energies of the light and absorb certain wavelengths (pigments).
Here, again, you have read some stuff and are trying to regurgitate in your own words. It's not really working. There is a continuous range of possible frequencies. Each frequency is associated with a different photon energy. Photons aren't "steps". This would be like saying that a piece of string is 'made up of inches'. Yes, you can say that it is possible to give a length to the nearest inch but that's all. The term 'spectrum' just refers to the relative intensity levels over a (continuous) range of frequencies.
All things emit some EM radiation - not necessarily light, as it depends on their temperature. Plenty of natural sources of light are not 'hot'. Stars etc are hot enough but cold clouds of gas can absorb and re-emit light of specific frequencies in our direction. And why 'ignore chemical light'? It follows the same rules as 'thermally generated light'. You are trying to over simplify to no real purpose. As for the appearance of paper in the light or in the shade- the light that comes from it varies under different circumstance. Your BRAIN works overtime to give you the impression that it is still the same piece of paper and it even does a fair job of colour correction to allow for time of day, or varying illumination. What you 'see' is not a measurement. For that, look at what you get on a digital camera that has all its controls set to 'manual'. That is more of a proper measurement.
