Asked by: Michelle May

X=(2Wnk)/c=(4Pik)/L

Where x is the absorption coefficient,W the frequency of light in the vacuum, c the speed of light in vacuum, l is the wavelength inside the medium and n and k are the refractive index and the attenuation index (also called extinction coefficient) respectively. The quantities n and K may be easily be expressed in terms of the material constants (dielectric constant, the electrical conductivity and the magnetic permeability)

Note that this expression of the absorption coefficient is a good approximation if the dielectric constant is real and the excitation frequency is low (long wavelength)

Answered by: Alex Bouhelier, Ph.D Physics, Uni Basel (CH)

'Physics is mathematical not because we know so much about the physical world, but because we know so little; it is only its mathematical properties that we can discover.'**Bertrand Russell**

(*1872-1970*)

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