Lens with Half Painted Black · CAP 2016 #Q22
Physics · optics
Problem
The lens shown below constructs a real image (B) of the arrow (A) on the screen (S). What will happen to the image if we paint the upper half of the lens black? a) The image will get inverted. b) The upper half of the image will disappear. c) The lower half of the image will disappear. d) The shape of the image will remain the same and will only get dimmer.Intuitive explanation
This problem tests your understanding of how a lens forms images through all of its surface. Every point on the lens contributes a complete ray path to every point on the image—blocking part of the lens doesn't erase part of the image, it just reduces the total light collected. Think of it like dimming a lightbulb: fewer photons arrive, but the same picture still forms. The key insight is that image formation depends on the geometry of refraction, not on having every region of the lens active.
Intuitive explanation
This problem tests your understanding of how a lens forms images through all of its surface. Every point on the lens contributes a complete ray path to every point on the image—blocking part of the lens doesn't erase part of the image, it just reduces the total light collected. Think of it like dimming a lightbulb: fewer photons arrive, but the same picture still forms. The key insight is that image formation depends on the geometry of refraction, not on having every region of the lens active.