Question.
Where should an object be placed in front of a convex lens to get a real image of the size of the object ?
(a) At the principal focus of the lens
(b) At twice the focal length
(c) At infinity
(d) Between the optical centre of the lens and its principal focus.
Where should an object be placed in front of a convex lens to get a real image of the size of the object ?
(a) At the principal focus of the lens
(b) At twice the focal length
(c) At infinity
(d) Between the optical centre of the lens and its principal focus.
solution:
When an object is placed at $2 \mathrm{~F}_{1}$ in front of a convex lens, its image is formed at $2 \mathrm{~F}_{2}$ on the other side of the lens. The image formed is real, inverted, and of the same size as the object. Thus, option (b) is correct i.e., the object should be placed at twice the focal length from the optical centre of the lens.
When an object is placed at $2 \mathrm{~F}_{1}$ in front of a convex lens, its image is formed at $2 \mathrm{~F}_{2}$ on the other side of the lens. The image formed is real, inverted, and of the same size as the object. Thus, option (b) is correct i.e., the object should be placed at twice the focal length from the optical centre of the lens.
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