NCERT Solutions Curiosity Chapter 10 .4 What Is a Lens? — Activity 10.8: Let us explore
Book page 16210 Updated on2026-09-05
Q1.
Examine the water drop. What is the shape of its surface? Is it flat or curved inward or curved outward?
Answer
The surface of the drop is curved outward — it bulges upward like a tiny dome. It is neither flat nor hollowed inwards.
Why the thin film of oil or wax matters: on bare glass water spreads out into a flat film, and a flat film would change nothing. Oil or wax stops the water from wetting the glass, so the drop pulls itself into a rounded bead instead of spreading — and it is that outward bulge which makes it behave like a lens.
Tip: a smaller drop bulges more sharply than a large one, and a more sharply curved surface magnifies more. Try two drops of different sizes side by side.
Q2.
Now, look down through the water drop at the text below. Do you find some change in the size of the letters just below the water drop? Do they look enlarged or smaller?
Answer
Yes — the letters under the drop look clearly enlarged, bigger than the very same letters lying just outside the drop.
Why the drop magnifies: the drop is a piece of transparent material with a surface curved outward — thicker at its middle than at its edge. That is precisely the shape of a convex lens. It bends the light coming up from the printed letter inwards, and your eye, tracing those bent rays back in straight lines, places the letter at a size larger than it really is.
Did you know? A magnifying glass (Fig. 10.14) is doing exactly what this drop of water does — it is simply a bigger, permanent version made of glass.