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Please tell me specifically how the colors reflect, and absorb heat?
Question Date: 2016-03-22
Answer 1:

Great question! This kind of question can help you learn a lot about how the world works.

The light that the Sun shines, which we call white light, is actually made up of many kinds of light. These include light with each color of the rainbow, and even some types of light we can't see, like ultraviolet light and infrared light. A good way to tell all of these types of light apart is by using their wavelength. For example, light with a wavelength of 400 nanometers is violet, and light with a wavelength of 700 nanometers is red. Why am I telling you about light when you asked about heat? Well, when a surface absorbs light, it becomes heat.

Now think about light hitting the surface of something. Surfaces deal with different types of light in different ways. You can think about it like this. A surface has a list of what to do with each type of light. One list might say: if the light is 400 nanometers, reflect all of it, and if it's not 400 nanometers, absorb all of it. When the Sun shines light on it, this surface will get hotter from absorbing many kinds of light. Only the part of the sunlight that is 400-nanometer light is not absorbed. (That light will bounce off the surface and some of it will reach your eye, letting you see that the surface is violet.)

Here's my summary. Light comes in many types, including each color of the rainbow. When each type of light hits something, the surface decides what to do with it. If the surface absorbs the light, the surface will heat up. If the surface reflects the light, you will see that color.


Answer 2:

Light comes in different colors. The color you see is the color of the light that hits your eyes. This means that anything that absorbs a color will not look that color - it will appear to have a different color. Anything that reflects a color will look that color. White, gray, and black are not colors, though: white reflects all colors, black absorbs all colors, and gray reflects some and absorbs some of all colors.

Light is energy. Any light that is absorbed, of any color, becomes heat. Thus something that reflects a color will not absorb it, and so will not be heated by it, but it will be heated by other colors that it does absorb.


Answer 3:

An interesting question, and the answer might surprise you! Colors themselves do not reflect or absorb heat. Rather, color is a consequence of a much more general phenomenon involving reflection or absorption. To see what I mean, there are two main ideas I'd like to convey: 1) thinking more generally about electromagnetic radiation and separating that from the notion of heat, and 2) the electronic structure of atoms.

The Electromagnetic Spectrum:
Your description of materials interacting with heat is part of a larger type of interactions involving light and matter. Light, also known as electromagnetic radiation, exists as a whole spectrum of energies, known as the electromagnetic spectrum .

You might be familiar with a types of electromagnetic spectrum, such as microwaves or x-rays. These are in fact all light that differ by how energetic it is. A tiny sliver of the electromagnetic spectrum is the visible spectrum, which is the range of energies (equivalent to thinking in terms of wavelength or frequency) that humans are able to see (i.e., as color). Just below the visible range is the infrared range. If you were hit by infrared waves, you would feel that as heat. However, heat itself is not a form of light but a form of energy. The infrared waves would excite molecules in your body that would dissipate that electromagnetic energy into thermal energy (i.e., heat).

In learning about the electromagnetic spectrum, we can say that colors and heat are two different things along the same electromagnetic spectrum, so one doesn't lead the other. The question is how is the electromagnetic spectrum related to absorption and reflection?

Interactions between light and matter:
This questions now delves into how light can interact with matter. Matter is composed of tiny components called atoms. Atoms are composed of even smaller components called electrons, protons, and neutrons. If you ever study particle physics, it turns out you can decompose those further into other subatomic particles. You'll learn (if you haven't already) that the nucleus is composed of protons and neutrons, and the number of protons is linked with the elemental identity of that atom (e.g., if it is phosphorus versus hydrogen). Around this nucleus is a cloud of electrons; something like this (not exactly, but it gets the point).

Figuring out that the structure of the atom was no small task, and has an interesting history if you're interested. We're going to be mostly worried about the electrons: Reflection and absorption are a consequence of light interacting with the electrons of a material.

We've already mentioned one interaction of light with matter- heat dissipation through the vibrations of atoms (specifically, the nuclei) in matter- but delves into a different story for another time.

It turns out that electrons occupy specific energies around the nucleus; this is a consequence of quantum mechanics. Because of this fact, only certain energies can excite the electron from a lower energy level to a higher energy level. That is, only certain energies (i.e., frequencies, wavelengths) of light can lead to the electron absorbing that energy. Other energies will pass through, i.e., be transmitted. The combination of frequencies of light that is absorbed or transmitted results in color if the wavelengths of light lay within the visible range of the electromagnetic spectrum. Reflection is slightly different but still involves electrons.

Hope this helps!
Best,


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