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_1, when the space between the two lenses is filled with glycerin (which has the same refractive index (mu = 1.5) as that of glass) then the equivalent focal length is F_2. The ratio F_1 :F_2 will be :

Two similar thin equi-convex lenses, of focal length f each, are kept

1.	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_1, when the space between the two lenses is filled with glycerin (which has the same refractive index (mu = 1.5) as that of glass) then the equivalent focal length is F_2. The ratio F_1 :F_2 will be :
Answer» `3:4` `2:1` `1:2` `2:3` SOLUTION :`(1)/(F_1)=1/f+1/f=2/f` `THEREFORE F_1=f/2` and `F_2=f` GIVEN `therefore(F_1)/(F_2)=1/2`

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