|MadSci Network: Physics|
In a word or two, I think you are dealing with absorbtion and reflection, with heat capacity thrown in on the side. Any object has the property that it reflects a portion of each color of light (Color is our perception. What is really varying is the wavelength of the light.) and absorbs the rest. Every material has different reflective properties; this is due to the interaction of the internal electromagnetic fields of the substance (from its atoms, and how its electrons are bonded) and the photons (which are the carriers of electromagnetic forces) coming in. It is a little difficult to explain this further without getting into a lot of difficult technical jargon and solid state physics. I'll take a shot at it, but if the next paragraph ends up confusing you rather than providing enlightenment, just skip it and go on to the following paragraph. Most materials exhibit what is called a bandgap, which means that no electrons in it can have energies between two levels (thus, a gap in the energy spectrum). If an incoming photon has an energy greater than the width of the bandgap, then it is likely to be absorbed. It will interact with an electron and find it has enough energy to boost it up past the bandgap into what is called the conduction band. Photons with lower energies tend to be far less likely to be absorbed and either pass through (transparent) or are reflected. If the particular material you are attempting to heat is reflective or transparent at the wavelength of the incoming light you are shining on it, it is unlikely to heat very much. If it is not reflective, then the energy of the photons is absorbed. Now, some may be reemitted at any wavelength longer than the incoming wavelength, and the rest will appear as heat. How much is reemitted and how much is converted to heat is a function of the material. For example, I happen to have several fluorescent mineral specimens. When I shine ultraviolet (short wavelength) light on them, they re-emit some of that energy as visible light (all visible light photons have longer wavelengths than ultraviolet photons) that I can then see. But only a small part of the ultraviolet is converted to visible light. Some materials have only a very faint fluorescence, but others can be bright enough to actually see print. Some of the minerals, one feldspar in particular, are very reflective in the ultraviolet...so much so that it hurts your eyes to look at the specimen when the ultraviolet lamp is shining on it. Now, once some of the incoming photons are converted to heat, how hot the substance gets depends on another material property, its heat capacity. Some materials, like metals, take relatively little energy to heat to a certain temperature. Others, like water, take a lot. What's going on here is that in the low heat capacity materials (metals), it is easy to get something (usually electrons) bouncing around real fast. In higher heat capacity materials (water), the energy can be stored in myriad ways like the vibration of bonds or rotation of molecules, that do not contribute to what we sense as heat. Almost everything discussed above is in the realm of what is known as solid state physics. This subject is not an easy one, and I don't know of a reference that isn't math-intensive above your likely level of mathematical ability (judging from your grade in school). The classic text is Kittel's "Solid State Physics", but I don't recommend that you go out and try this book as it is formidable. Rosenberg's book in the Oxford Physics series, title "The Solid State" is somewhat more approachable but still beyond a high school level. I don't actually know of an easy introduction to solid state physics, which perhaps reflects its level of difficulty.
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