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Asked in Odisha NEET 2019 · Lens maker's formula and power
Given: an equi-convex lens of power P, sliced by a plane containing the principal axis.
Idea: power comes from the lens maker's formula, which contains only μ and the two radii — never the size of the piece of glass.
The cut runs along the axis, so each half still carries both original surfaces with their original radii.
1/f=(μ-1)(1/R-1/(-R)) is therefore unchanged for each half.
So each half still has power P; only the aperture is halved, which dims the image without moving it.
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