A convex lens of focal length 15 cm produces a magnification of +4. The object is placed:(a) at a distance of 15 cm (b) between 15 cm and 30 cm(c) at less than 15 cm (d) beyond 30 cm
(c) At less than 15 cm
Explanation
Since, the magnification of the image is positive, it means the nature of the image is virtual and erect. Also, size of the image is more than 1 which is 4, it implies that the size of the image is magnified (enlarged).
Thus, the image of this nature and size is formed when the object is placed within the focus $F'$ or between the focus $F'$ and optical centre $C$ of the convex lens.
Here, the focal length $f$ is 15 cm, so the object should be placed at less than 15 cm.
Image is posted for reference only
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