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If a lens is divided into two equal halves, the optical power of each segment remains unchanged because the focal length does not alter.

1. 1/f = (μ − 1) [1/R1 − 1/R2]
2. 1/25 = (1.5 − 1) [1/2R − 1/2R]
3. 1/25 = 0.5 (3/2R)
4. 2R = 37.5 cm, R = 18.75 cm

Correct answer: 1/f = (μ − 1) [1/R1 − 1/R2]

Solution

When a lens is cut into two halves, either along the principal axis or perpendicular to it, the focal length of each half remains the same as the original lens. Hence, the power of each half also remains the same. Option A represents the lens maker's formula, which is relevant here.

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