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 F₁. When the space between the two lenses is filled with glycerin (which has the same refractive index (μ = 1.5) as that of glass) then the equivalent focal length is F₂. The ratio F₁ : F₂ will be : 

(1) 2 : 1 

(2) 1 : 2 

(3) 2 : 3 

(4) 3 : 4

Comments

Ray optics and optical instruments