2021 · Q4
An object is placed 10 cm in front of a lens. The image formed is real, inverted and of same size as the object. What is the focal length and nature of the lens?
general-sciencephysics-light-electricity
- A5 cm, converging
- B10 cm, diverging
- C20 cm, converging
- D20 cm, diverging
Explanation
A real, inverted image of the same size as the object forms only when the object is placed at 2F (twice the focal length) of a convex, i.e. converging, lens. Since the object distance is 10 cm, 2F = 10 cm and the focal length F = 5 cm. A diverging (concave) lens can never form a real image. Hence the lens has a 5 cm focal length and is converging.