We have a monochromatic plane wave with a frequency ω=10^15 (1/s). It is spread in a medium whose resonance frecuency is also ω=10^15 (1/s). The wave is attenuated in the spreading direction. In 1 cm, the electric field of the wave is 10 times smaller. Give an expression for the extinction index (K) (imaginary part of refractive index). I know the expression for K(ω) in the special case that the wave's frequency is equal to the medium's resonance frequency. The problem is that I don't know what to do with the other data: 'In 1cm, the electric field of the wave is 10 times smaller'.