PHYSICS · Single correct · AP · Physics 2: Algebra-based · Geometric Optics · Geometric Optics
Problem
For a thin concave lens in air, which statement correctly identifies the sign of its focal length when the standard sign convention is used?
(a) Positive, because concave surfaces cause light rays to converge to a real focal point.
(b) Positive, because virtual distances are taken as positive in the lens sign convention.
(c) Negative, because the focal point lies on the same side as the incident light.
(d) It depends on the object distance; the focal length is positive for close objects and negative for distant ones.