The image of an object formed by a lens is of magnification -1. If the distance between the object and its image is 60 cm, what is the focal length of the lens? If the object is moved 20 cm towards the lens, where would the image be formed? State reason and also draw a ray diagram in support of your answer.

The image of an object formed by a lens is of magnification -1. If the

1.	The image of an object formed by a lens is of magnification -1. If the distance between the object and its image is 60 cm, what is the focal length of the lens? If the object is moved 20 cm towards the lens, where would the image be formed? State reason and also draw a ray diagram in support of your answer.
Answer» SOLUTION :Image with magnification -1 MEANS image is inverted and of the same size. Therefore, object is at 2 F and the image is also at 2F on the other side of the lens. Therefore, distance between the object and its image is 4f=60 cm `impliesf=15cm` Object distance 2f=30 if the object is shifted towards the lens by 20 cm , the new object distance =30 cm - 20 cm =10 cm This distance is less than the FOCAL length and the image formed in this CASE would be virtual, erect and will form on the same as the object.