The Equi-convex Lens, Shown In The Figure, Has A Focal Length f. What Will Be The Focal Length Of Each Half If The Lens It Cut Along AB? (See Fig.)                                                                    

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The equi-convex lens, shown in the figure, has a focal length f. What will be the focal length of each half if the lens it cut along AB? (See fig.)



Correct option is



For equi-convex lens R1 = –R2, so that  


If the lens is cut along AB, we have two plano convex lenses. For a plano convex lens, R2 = ∞. Therefore, its focal length f’ is  





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