# EM penetration

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As grotesque as the title may appear to suggest, I basically want to understand just that. Why is it that EM radiation of each group of wavelengths (visible, IR, UV etc.) manages to penetrate materials with varying ease. From what I've seen so far - and I haven't studied this directly, I'm just curious - there doesn't seem to be any consistency with the relationship between the wavelength of the radiation and the penetrating ability with each material.

e.g. light passes through the atmosphere very well, while the shorter wavelength UV radiation has a much harder time getting through the atmosphere. So from this statistic, it might be concluded that shorter wavelength radiation cannot penetrate matter as well. However, gamma radiation manages to go through much thicker metals than any other longer wavelength types.

So, is the penetrating ability of each group of radiation dependant upon the material and its properties (because the gases in the atmosphere shouldn't be strictly compared to a metal) or is it dependant upon the properties of each wavelength of radiation?

## Answers and Replies

So, is the penetrating ability of each group of radiation dependant upon the material and its properties (because the gases in the atmosphere shouldn't be strictly compared to a metal) or is it dependant upon the properties of each wavelength of radiation?
yes...meaning it's how the waves and materials interact together.

Likely you want to get some information on permittivity......

via wikipedia:
Permittivity is a physical quantity that describes how an electric field affects, and is affected by, a dielectric medium, and is determined by the ability of a material to polarize in response to the field, and thereby reduce the total electric field inside the material. Thus, permittivity relates to a material's ability to transmit (or "permit") an electric field.
also see the section there about complex permittivity....

and you might also find nuclear magnetic resonance of interest: http://en.wikipedia.org/wiki/Nuclear_magnetic_resonance

" A key feature of NMR is that the resonance frequency of a particular substance is directly proportional to the strength of the applied magnetic field..."