The plane faces of two identical plano-convex | vedclass

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(C) When two identical plano-convex lenses,each with focal length $f$,are joined by their plane faces,the effective focal length $F$ of the combinatio

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$f$

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(C) When two identical plano-convex lenses,each with focal length $f$,are joined by their plane faces,the effective focal length $F$ of the combination is given by the lens combination formula: $\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2} = \frac{1}{f} + \frac{1}{f} = \frac{2}{f}$.Thus,the focal length of the resulting convex lens is $F = f/2$.For a convex lens,an image of the same size as the object is formed when the object is placed at a distance of $2F$ from the optical centre.Substituting the value of $F$,the required distance is $2 	imes (f/2) = f$.

The plane faces of two identical plano-convex lenses,each with focal length $f$,are pressed against each other using an optical glue to form a convex lens. The distance from the optical centre at which an object must be placed to obtain an image of the same size as the object is

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