Question:
If the power of a lens is +4 D, then the lens is a
If the power of a lens is +4 D, then the lens is a
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A positive power indicates a convex lens and a negative power indicates a concave lens. The focal length is the reciprocal of the power.
Updated On: Apr 7, 2026
- convex lens of focal length 25 cm
- concave lens of focal length 25 cm
- concave lens of focal length 40 cm
- convex lens of focal length 50 cm
- concave lens of focal length 20 cm
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The Correct Option is A
Solution and Explanation
Step 1: The power \( P \) of a lens is related to its focal length \( f \) by the formula:
\[ P = \frac{1}{f}, \quad \text{where} \quad P \text{ is in diopters (D) and } f \text{ is in meters}. \]
Step 2: Given that \( P = +4 \, D \), we can find \( f \) as:
\[ f = \frac{1}{P} = \frac{1}{4} = 0.25 \, \text{m} = 25 \, \text{cm}. \]
Since the power is positive, the lens is a convex lens.
Thus, the lens is a convex lens with a focal length of 25 cm.
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