The following animation shows what happens when a plane-polarized wave traverses a medium that absorbs light but does not refract it (its refraction index is 1). A piece of material is shown, with an intersecting plane both in front and behind it. We measure the field vector where the light beam intersects these two intersecting planes.
The following animation shows the intersecting planes looked at from the front. On the left, the light beam in its original state; on the right, the light beam after crossing the piece of material.
As you can see, when the light enters the medium, it becomes fainter, i.e. its intensity decreases according to an exponential function inside the medium. After exiting the material, the field vector oscillates the same way as before entering it but its amplitude is only about 36% of the earlier value.