A concave and a convex lens have the same foc | vedclass

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(C) The focal length of a convex lens is $f_1 = +20 \ cm$ and that of a concave lens is $f_2 = -20 \ cm$.When placed in contact,the equivalent focal l

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Of the same size as the object and erect

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(C) The focal length of a convex lens is $f_1 = +20 \ cm$ and that of a concave lens is $f_2 = -20 \ cm$.When placed in contact,the equivalent focal length $F$ is given by the formula: $\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2}$.Substituting the values: $\frac{1}{F} = \frac{1}{20} + \frac{1}{-20} = 0$.This implies $F = \infty$.$A$ lens combination with an infinite focal length acts as a plane glass slab.For a plane glass slab,the magnification $m = +1$.Therefore,the image formed is of the same size as the object and is erect.

$A$ concave and a convex lens have the same focal length of $20 \ cm$ and are put into contact to form a lens combination. The combination is used to view an object of $5 \ cm$ length kept at $20 \ cm$ from the lens combination. As compared to the object,the image will be

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