If a cloud lying between a star and an observer has an average absorption coefficient of a = 3.0 x 10^-13 cm^-1 (that varies throughout the cloud), a thickness of s = 2.0 x 10^13 cm and an optical depth of t = 7 along the line of sight, the intensity of the light will be: (a) reduced by a factor of e^-3.0x10", (b) reduced by a factor of 3.0 x 10^-13 (c) reduced by a factor of e^-6, (d) reduced to zero, (e) reduced by a factor of e^-7 (f) not enough information, one needs to know the details of how the density varies along the line of sight.
If a cloud lying between a star and an observer has an average absorption coefficient of...