3.14 As noted in Section 3.1, the power in a light beam is proportional to the square of its electric field, and the electric field for a beam traveling in

an attenuating medium can be given by Eq. (3.8). The attenuation coefficient in that equation determines the loss. On the other hand, we more frequently discuss the loss in terms of decibels per kilometer.Show that the power change in dB/km and the attenuation coefficient a are related b yy = -8.685a, where a is given in the units km.