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

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Of the same size and erect

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(C) The focal length of a convex lens is $f_1 = +20 \ cm$ and the focal length of a concave lens is $f_2 = -20 \ cm$.When placed in contact,the equivalent focal length $F$ is given by $\frac{1}{F} = \frac{1}{f_1} + \frac{1}{f_2}$.Substituting the values: $\frac{1}{F} = \frac{1}{20} + \frac{1}{-20} = 0$,which implies $F = \infty$.$A$ combination with infinite focal length acts as a plane glass plate.$A$ plane glass plate forms a virtual,erect image of the same size as the object at the same distance behind the plate.

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

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