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Name: Katherine
Status: educator
Grade: 9-12
Country: USA
Date: Summer 2012

Why are some regions of the electromagnetic spectrum shown to overlap on illustrations? For example, x-rays and gamma rays; infrared and microwaves; and microwaves and radio waves are typically shown to overlap on illustrations in high school textbooks. I thought that the electromagnetic spectrum was divided into regions by wavelength, but clearly this is not the case. Some resources I've found suggest that the overlap has to do with the source of the energy. That's fine for waves generated on Earth, but how then do you tell the boundary between an x-ray and gamma ray generated by the sun? I can't imagine when the source is the sun, the regions overlap.

You have to be aware that the electromagnetic spectrum is continuous. Where you “draw the line” to apply a name to a particular range is to some extent arbitrary. The limits of various parts of the electromagnetic spectrum are arbitrary.

Vince Calder

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