Question

When the image is virtual and erect in the case of a convex lens, is the focal length still positive, or does it becomes negative?

Answer 1

Answer: I hope it helps!!!

Explanation: The focal length of a convex mirror is always positive as per the new Cartesian convention. It does not depend on the type of image. Further, a convex mirror always produces a virtual image. So, adding the clause “when the image formed is virtual” does not provide any additional information in case of convex mirrors.In case of a convex lens, the focal length is always positive. It does not depend on the type of image. A convex lens produce a real image if the distance of the object from the lens is greater than the focal length and a virtual image if the distance of the object from the lens is lesser than the focal length. This type of image has no bearing on the focal length.