MadSci Network: Physics

Re: Why radio waves can pass through a wall but light waves can't ?

Date: Tue Jun 7 10:37:06 2016
Posted By: Benn Tannenbaum, Program Director
Area of science: Physics
ID: 1460516059.Ph

Good question!

First, let's start with some terms. You talk about the power of the different wavelengths of light; a better unit is energy, as power is energy per second and doesn't make as much sense in this context. (Unless, of course, you're trying to bore a hole through the wall and you want to know how long it would take....)

Visible light has a wavelength of between 400 and 700 nm. Atoms are less than 1/10th of a nm in diameter, meaning the wavelength of visible light is about 1000 times larger. Radio waves have a wavelength of 1mm to 100 kilometers-- much much larger. Visible light is able to interact with the matter that constitutes the wall; some is absorbed and some is reflected. The reflected light is what gives the wall its color. The radio wave, on the other hand, passes through the wall without interacting because the atoms in the wall are so small compared to the wavelength of the radio wave. (There is a little bit of interacting, mostly scattering, that happens with radio waves which is why cell phones don't work well underground or inside structures that have lots of metal supports.)

Hope this helps!

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