Question:medium

A double-convex lens of power \( P \), with each face having the same radius of curvature, is cut along its principal axis. The two parts are arranged as shown in the figure. The power of the combination will be: \includegraphics[width=0.3\linewidth]{14image.png}

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- When a convex lens is cut along its principal axis, each half acts as a plano-convex lens.
- The focal length of each part is halved, and since power is inversely proportional to focal length, the power of each part doubles.
- The total power of the combination is the sum of individual powers, making it \(2P\).
- This concept is useful in understanding how lens cutting affects optical power in practical applications.
Updated On: Feb 17, 2026
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Solution and Explanation

Upon bisecting a double-convex lens along its principal axis, each resultant segment functions as a plano-convex lens. The focal length of these segments is reduced by half. Given that optical power is reciprocally proportional to focal length, halving the focal length results in a doubling of the power for each segment. When these two segments are rejoined, their powers are additive. Consequently, the aggregate power of the combined lens is: \[P_{\text{total}} = P + P = 2P\] This establishes that the power of the combined lens is \(2P\). Therefore, the definitive answer is: \[\boxed{2P}.\]
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