Thomas Wedgwood

Quantization of Energy (Thomas Wedgwood)

It is common knowledge that objects give off light when heated. Examples range from the gentle red glow of an electric burner on a stove to the bright white light emitted when the tungsten wire in a light bulb is heated by passing an electric current through the wire. What is less well known is a phenomenon discovered by Thomas Wedgwood in 1792. Wedgwood, whose father started the famous porcelain factory, noticed that many objects give off a red glow when heated to the same temperature. The bottom of a crucible and the iron triangle on which the crucible rests, for example, both glow red when heated with a bunsen burner.

Wedgwood also noticed that the color of the light emitted by an object changes as it is heated to higher temperatures until the object glows white hot, but the spectrum of light given off at a particular temperature is the same for any object. The fact that sunlight is equivalent to the light emitted by an object at 6000 K, for example, has led to the assumption that this is the temperature of the surface of the sun.


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Wedgwood's observation that objects heated to the same temperature give off light of the same color can be illustrated by comparing the light given off by a crucible and the iron triangle on which it rests when the crucible is heated.


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