Question

..
Two similar thin equi-convex lenses, of focal length
f each, are kept coaxially in contact with each
other such that the focal length of the combination
is F. When the space between the two lenses is
filled with glycerine (which has the same refractive
index (u = 1.5) as that of glass) then the
equivalent focal length is F2. The ratio F1: F2
will
be :
[NEET - 2019]
(1) 2:1
(2) 1:2
(3) 2:3
(4) 3 : 4​

Answer 1

Answer:

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