Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 30 - Think and Explain: 74

Answer

Red.

Work Step by Step

Objects at any temperature greater than absolute zero will emit radiation. The peak frequency of this radiation is proportional to the object's absolute temperature - the hotter the object, the higher the frequency of the peak radiation. At room temperature, the metal radiates mostly in the infrared portion of the electromagnetic spectrum, which has a frequency below that of visible light. This radiation is invisible to the naked eye. As the metal is heated up, it emits more radiation at all frequencies, and the frequency peak of that radiation moves upward into the visible part of the spectrum. Red is the color with the lowest frequency (and the longest wavelength), so it is the first visible color. The metal first glows red-hot.
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