Two unknown thin lenses are tested with a parallel beam of light

PHYSICS · Single correct · AP · Physics 2: Algebra-based · Geometric Optics · Geometric Optics

Problem

Two unknown thin lenses are tested with a parallel beam of light. • Lens A produces a small bright spot 15 cm beyond the lens on the side opposite the beam. • Lens B produces rays that exit the lens spreading apart as if they had originated 10 cm in front of the lens. Which of the following identifies the type and focal-length sign of each lens? (a) Lens A: converging, f=+15 cmf=+15\,\text{cm}; Lens B: diverging, f=+10 cmf=+10\,\text{cm} (b) Lens A: diverging, f=−15 cmf=-15\,\text{cm}; Lens B: converging, f=+10 cmf=+10\,\text{cm} (c) Lens A: converging, f=+15 cmf=+15\,\text{cm}; Lens B: diverging, f=−10 cmf=-10\,\text{cm} (d) Lens A: converging, f=−15 cmf=-15\,\text{cm}; Lens B: diverging, f=−10 cmf=-10\,\text{cm}

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