Electromagnetic waves have oscillating electric and magnetic fields perpendicular to each other and to the propagation direction. They are transverse and can travel through a vacuum. In vacuum every electromagnetic band travels at c=3.00×108m/s, so c=fλ. A shorter vacuum wavelength means higher frequency, not a greater vacuum speed.
In increasing frequency, the broad sequence is radio, microwave, infrared, visible, ultraviolet, X−ray and gamma ray. Band boundaries are approximate and labels can also depend on production processes. Visible light is only a small part of the spectrum. Match a stated application to its band, such as radio communication, infrared thermal imaging or X−ray imaging, without assuming all electromagnetic radiation has identical interactions with matter.
Example 1
Find the vacuum wavelength of a 100 MHz radio wave. Use c=3.00×108m/s.
f=1.00×108 Hz. λ=fc=3.00m.
Example 2
Find the frequency of vacuum light with wavelength 600 nm. Use c=3.00×108m/s.
λ=6.00×10−7m. f=λc=5.00×1014 Hz.
Watch out: Both travel at c in vacuum. Their frequencies and wavelengths differ.