Read the following passage and answer the questions.
Aman sets up a thin convex glass lens of focal length 20 cm on an optical bench. He places a lighted candle on one side of the lens and a white screen on the other side. He moves the candle to several positions. Each time, he slides the screen until a sharp image of the flame appears on it. For some positions of the candle, no image can be caught on the screen at all. He then removes the screen and looks at the candle through the lens. In one trial, he places the lens in a glass tank filled with water. In another trial, he places a thin concave lens in contact with the convex lens and looks for the new image. His teacher asks him to note the image distance and the size of the image each time. She also asks him to write the power of each lens in dioptre.
When the concave lens is placed in contact, the candle is beyond the focus of the convex lens. To find the final image, the real image formed by the convex lens alone is treated, for the concave lens, as
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → a virtual object
For lenses in contact, the image formed by the first lens is used as the object for the second lens. The rays from the convex lens are still converging when they reach the concave lens. They never meet at the first image point.
Option (1) a virtual object — Correct. The rays move towards the image point of the convex lens but reach the concave lens first. For the concave lens they come towards a point behind it, so that point is a virtual object.
Option (2) a real object — Incorrect. A real object sends diverging rays to the lens from a point in front of it. Here no rays actually start from that point.
Option (3) the final image of the combination — Incorrect. The image of the first lens is used only to find the final image. The final image is formed by the concave lens.
Option (4) a virtual image of the candle — Incorrect. The convex lens alone would form a real image here, because the candle is beyond its focus.
NCERT (2026-27):
Combination of thin lenses in contact – “… The first lens produces an image at I1. Since image I1 is real, it serves as a virtual object for the second lens B, producing the final image at I. It must, however, be borne in mind that formation of image by the first lens is presumed only to facilitate determination of the position of the final image.”