Answer: +2.5 D
\[P = \frac{1}{f} = \frac{1}{0.40\ \text{m}} = +2.5\ \text{D}\]
The focal length must be taken in metres, and the power of a convex (converging) lens is positive.
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Doubtly AI
· 25 Oct 2026
AI-verified · Oct 2026
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