Two similar thin equiconvex lenses, of focal length each, are kept coaxially in contact with each other such that the focal length of the combination is . When the space between the two lenses is filled with glycerine (which has the same refractive index, , as the glass) then the equivalent focal length is . The ratio will be:
PhysicsNEET 2019Reflection and refraction, mirror and lens formulae
Ray Optics and Optical Instruments
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