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प्रश्न
Calculate the focal length of a corrective lens having power +2.5 D.
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उत्तर
Solution: Data: Convex lens, P = +2.5 D, f = ?
P = 1/f
∴ 2.5 D = 1/f
∴ f = 1/2.5D = 0.4m = 40cm
The focal length of the lens is 40 cm.
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