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)

'There is no inductive method which could lead to the fundamental concepts of physics. Failure to understand this fact constituted the basic philosophical error of so many investigators of the nineteenth century.'**Albert Einstein**

(*1879-1955*)

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