Take a moment to carefully examine Figure 21.2. It is the analysis of blackbodies that led to one of the most consequential discoveries of the twentieth century. This container is a good model of a perfect blackbody. In time, the hole would continue to glow but the light would be invisible to our eyes. Like a burner on your stove, the hole would glow red, then orange, then blue, as the temperature is increased. The hole may even begin to glow in different colors as the temperature is increased. As the temperature of this container gets hotter and hotter, the radiation out of this dark hole would increase as well, re-emitting all energy provided it by the increased temperature. Imagine carving a small hole in an oven that can be heated to very high temperatures. Imagine wearing a tight shirt that did this! This phenomenon is often modeled with quite a different scenario. It is likely best to refer to anything that is not a perfect blackbody as an approximation of a blackbody in order to avoid confusion.Ī perfect blackbody is one that absorbs and re-emits all radiated energy that is incident upon it. Occasionally, texts refer to blackbody and perfect blackbody as two different concepts. This shirt is a good approximation of what is called a blackbody. Black shirts, as well as all other black objects, will absorb and re-emit a significantly greater amount of radiation from the sun. You are likely aware that wearing a tight black T-shirt outside on a hot day provides a significantly less comfortable experience than wearing a white shirt. Our first story of curious significance begins with a T-shirt. Is a black piece of paper perfectly black?
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