Question

where should an object be placed in front of a convex lens to get a real image of the size of the object​

Answer 1

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At Centre of Curvature.

Answer 2

Anywhere except between Focus and Optical Center. It will produce a Real and Magnified Image. If you place the Object anywhere else :
1. At F
2. Between F' and 2F'
3. At 2F'
4. Beyond 2F'
5. Infinity.
The Image will be Real and Inverted but of Different Sizes.
To get an Image of same size, Object should be placed at 2F'.