WAEC Physics 2018 Paper

Concept:A thin converging lens forms a virtual, erect, and magnified image only when the object is placed within the focal length, that is, between the lens and its focus.Explanation:For a converging lens, the nature of the image depends on the object distance $u$ relative to the focal length $f$.When $u > 2f$, the image is real, inverted, and diminished.When $u = 2f$, the image is real, inverted, and same size.When $2f > u > f$, the image is real, inverted, and magnified.When $u = f$, no image is formed because the rays emerge parallel.When $u < f$, that is, when the object is placed between the optical centre and the focus, the rays appear to diverge from a point behind the lens.Hence, the image formed is virtual, erect, and magnified.Thus the object must be placed between the focus and the lens.Answer:Option A: between the focus and the lens.