# Absorbance by using Poynting vector

How should I compute the amount of energy of an EM wave absorbed by a material? Can I just use the divergence of the Poynting vector?

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Welcome to physics SE. What have you tried to solve this problem? –  Stefan Bischof Mar 6 '13 at 7:31
i tried joule heating, electrical conductivity times E square ， but it turns out bad, because it's kinda linearly proportion to electrical conductivity. but when the electrical goes up th like 10^7 , the power absorbed is obviously too high. as is for the poynting vector, the formula is Pabs=-0.5xReal(div(S)) where S is the poynting vector. but i don't have the imaginary part here. so I used div(S) only. I don't have the results yet ,the codes are still running but i got a bad feeling about it .:) thank you –  Duran Deng Mar 6 '13 at 9:57
Can you outline the setup a bit better? Is this a plane wave travelling in a medium that has a conductivity, or a wave incident upon the surface of such a substance? –  Rob Jeffries Aug 18 at 18:55