The problem gives the angular frequency of a light wave (w) is represented by e^iw(t-nx/c) it says that sometimes n is replaced by the complex quantity n-ik. The question asks what is the effect of k on the wave. Also, it asks, what is its physical signifigance? I tried substituting in for n-ik for n, and then multiplying in the iw. I got: e^ (iwt-iwnx +kx)/c So I see that the k term is the only real term in the exponent, however I am not sure how that effects the wave, or what its physical signifigance is.