The given lens is broken into four parts rearranged as shown. If the initial focal length is f, then after rearrangement the equivalent focal length is
A
f
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B
f2
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C
f4
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D
4f
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Solution
The correct option is Bf2 When a lens is spliced longitudinally (along the principal axis), the resulting two half-lenses have the same focal length as the original full lens.
i.e f(1+2)=f(3+4)=f
If the two halves are spliced transversely (perpendicular to principal axis), the focal length of each of their halves is doubled.
f1=f2=f3=f4=2f
Now, if 1, 2, 3 and 4 are stacked one after the other, net focal length is given by