How do you find the rough focal length of a convex lens? Is the same method applicable to a concave lens?
The rough focal length of a convex lens is obtained by forming sharp image of a very distant object on a screen. The distance of the screen from the lens gives us the rough focal length of the lens.
This method is not applicable to a concave lens, as image formed by a concave lens is virtual and it cannot be taken on a screen.
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