試題詳解

39. The howler monkey is the loudest land animal and, under some circumstances, can be heard up to a distance of 8.9 km. Assume the acoustic output of a howler to be uniform in all directions and that the threshold of hearing is W/m². A juvenile howler monkey has an acoustic output of 63 μW. What is the ratio of the acoustic intensity produced by the juvenile howler to the reference intensity I₀, at a distance of 200 m?
(A) 63
(B) 125
(C) 175
(D) 250
(E) 375