If a magnification of, $-$1 is to be obtained by using a converging lens of focal length 12 cm, then the object must be placed:(a) within 12 cm (b) at 24 cm (c) at 6 cm (d) beyond 24 cm

(b) at 24 cm

Explanation

Since, the magnification of the image is negative, it means the nature of the image is real and inverted. Also, size of the image is equal to 1, which implies that the size of the image is equal to the size of the object. 

Thus, the image of this nature and size is formed when the object is placed at $2f$ of the convex lens.

Here, the focal length $f$ is 12 cm, then the $2f$ will be 24 cm $(2\times {12})$, so the object should be placed at 24 cm.

Image is posted for reference only

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Updated on: 10-Oct-2022

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