試題詳解

49. Three thin lenses with focal lengths 0.1 m, 0.2 m, and 0.3 m are placed next to each other. What is the equivalent focal length of a single lens?
(A) 0.05 m
(B) 0.15 m
(C) 0.25 m
(D) 0.33 m
(E) 0.45 m