# One-half of a convex lens is covered with a black paper.

Question.
One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.

solution:
The convex lens will form complete image of an object, even if its one half is covered with black paper. Only the brightness of the image will reduce, in this case it will be half of the brightness of original image. It can be understood by the following two cases:

(a) Let the upper half of the lens be covered and an object be placed between optical centre and the focus $\mathrm{F}_{1}$. The light rays from the object falling on the lower half of the lens form a virtual, erect and magnified image [see fig.(a)]

(b) Let the lower half of the lens be covered and an object be placed between optical centre and the focus $\mathrm{F}_{1}$. The light rays from the object falling on the upper half of the lens form a virtual, erect and magnified image [see fig.(b)]

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