Physics

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\,\text{cm}

; Lens B: diverging,

f=+10\,\text{cm}

b) Lens A: diverging,

f=-15\,\text{cm}

; Lens B: converging,

f=+10\,\text{cm}

c) Lens A: converging,

f=+15\,\text{cm}

; Lens B: diverging,

f=-10\,\text{cm}

d) Lens A: converging,

f=-15\,\text{cm}

; Lens B: diverging,

f=-10\,\text{cm}

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