Introductory Physics Volume Two

7.4 Electromagnetic Waves 145
§ 7.4 Electromagnetic Waves
With our eyes we are able to see electromagnetic (EM) waves that
have wavelengths between about 400nm to 700nm. We experience light
with different wavelengths as different colors, as indicated in the following
table.
Wavelength Frequency Perceived Color
740 to 625 nm 405 to 480 THz red
625 to 590 nm 480 to 510 THz orange
590 to 565 nm 510 to 530 THz yellow
565 to 520 nm 530 to 580 THz green
520 to 500 nm 580 to 600 THz cyan
500 to 430 nm 600 to 700 THz blue
430 to 380 nm 700 to 790 THz violet
Note that the frequency and wavelength of an EM wave are related by
λf = c where c is the speed of light.
But this is only a small range of EM spectrum.
We see that there are a number of familiar items in the spectrum: x-
rays, microwaves, and radio waves are all EM waves. The range of
the spectrum just above and just below the visible range are called the
ultraviolet (UV) and infrared (IR). The prefixes ultra (above) and infra
(below) refer to the frequency not the wavelength.
⊲ Problem 7.6
Your microwave oven is filled with EM waves with a frequency of about
3 GHz. What is the wavelength of the wave? The microwave oven heats
up the objects in the oven, because the oscillating EM wave causes an
oscillating electric force on the electric dipoles in the object, which
causes the dipoles to oscillate. The frequency of a standard microwave