Figure A shows two identical plano-convex lenses in contact as shown.The combination has local length 24 cm.Figure B shows the same with a liquid introduced between them.If refractive index of glass of the lenses is 1.50 and that of the liquid is 1.60 , the focal length of the system in figure B will be
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Correct option is A)
Let radius of the convex side be R.
By lens makers' formula,
So focal length of 2 identical plano-convex lens is given by, f1=241=(1.5−1)(∞1−−R1)+(1.5−1)(R1−∞1)⟹R=24cm
The total focal length of the lens combination can be given as,