What is the focal length f of a thin lens having power P = +2.5 Diopters?
Answer and explanation
Correct answer: D. 0.40 m or 40 cm
- Step 1: Lens power P in diopters is related to focal length f in meters by P = 1 / f. Step 2. f = 1 / P = 1 / 2.5 = 0.40 m = 40 cm. Answer: 0.40 m or 40 cm. Why not the others: 2.5 m uses power value directly; 0.25 m calculates 1/4; 4.0 m has a decimal shift.
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