The magnification of an image formed by a lens is -1. If the distance of the image from the optical centre of the lens is 25 cm, where is the object placed? Find the nature and focal length of the lens. If the object is displaced 15 cm towards the optical centre of the lens, where would the image be formed? Draw a ray diagram to justify your answer.
CBSE FOREIGN - SET 1 2017
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- (m = -1, means that the image is real, inverted and of the same size as the object).
$\therefore\text{f}=\frac{25}{2}=12.5\text{cm}$
- Nature of the lens is convex/converging.
- On displacing the object distance by 15 cm, towards the lens, the object distance becomes 10 cm which is less than the focal length. Image formed now is virtual/same side of lens as the object.
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