Question

9.
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.



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Answer 1

Answer:

A point on the object needs only two rays to form an image. Since the entire lens is not covered, at least two rays from each point does pass through the lens and hence, image is formed. However, since the number of rays involved in the image formation reduces as the lens is covered, the image formed is of lesser intensity and less brighter.

Experiment:

Apparatus needed: convex lens, candle, two black sheets of paper.

Procedure:

Mount a lens on a table. Light a candle with a match stick and place it on one side of the lens on the table. Turn of the lights of the room so that it gets dark. Take the sheet of paper and place it on the other side of the lens as the candle. Now focus the image formed on the sheet of paper by moving the sheet only. Observe the image. Mark the positions of candle, lens and screen. Now, turn off the light. Take the lens and cover half of it with the second sheet of black paper. Mount the lens on the table in the original position and repeat the above experiment.

Observations:

A focussed image is obtained in both the experiments. However, the image formed with half the lens covered is less bright as compared to when it is uncovered.