Question

Large number of thin strips of black paper are made on the surface of a convex lens of focal length 20 cm to catch the image of a white horse. The image will be

• A. a zebra of black stripes
• B. a horse of black stripes
• C. a zebra of less brightness
• D. a horse of less brightness

Hint:

Covering any part of a lens never cuts off or alters the shape of the image.
It only reduces the amount of light passing through, which decreases the brightness of the complete image.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks about the nature of the image formed when a part of a convex lens is covered with thin, black paper strips while trying to capture the image of a white horse.

Step 2: Key Formula or Approach:
We use the principles of image formation by a lens. Every small section of a lens is capable of forming a complete image of an object.

Step 3: Detailed Explanation:

• To form a complete image of any point on an object, light rays from that point must pass through the lens and converge at the corresponding image point.

• When black paper strips are placed on the lens, they block the light rays falling on those specific covered portions.

• However, light rays from every part of the white horse can still pass through the remaining uncovered, transparent sections of the lens.

• These unblocked rays successfully converge to form a complete, continuous image of the white horse. No black stripes will appear on the horse itself.

• Since some of the light rays are blocked, the total amount of light energy reaching the screen to form the image is reduced.

• The reduction in light energy decreases the intensity or brightness of the final image.

• Hence, we get a complete image of the white horse, but it will have less brightness.


Step 4: Final Answer:
The image will be a horse of less brightness.