A convex lens forms a real and inverted image of a needle at a distance of 50 cm from the lens. Where is the needle placed in front of the convex lens, so that this image is of the same size as the object?

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1 Answers

Given, Distance of image, v = + 50 cm
Distanceofobject, u=?
Since the image is real, inverted and of the same size of the object, so object should be placed at the same distance (2f) on left side of lens. Thus,
v=2f=+50 cm
u= - 50 cm
f = +25 cm
(On the basis of new cartesian sign convention it is always considered as positive).

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