NCERT Solutions Curiosity Chapter 10 .4 What Is a Lens? — In-text Questions
Book page 16210 Updated on2026-09-05
Q1.
We explored the images of an object formed by curved mirrors. But how do objects look when viewed through transparent materials with curved surfaces?
Answer
They look changed in size, and if the surface is curved enough they can even look upside down — much as they do in a curved mirror, except that now we are looking through the material rather than in it.
Why there is any change at all: light bends when it passes from air into glass or water and again when it comes back out. At a flat surface every ray of a beam is bent in the same way, so the beam carries on with its shape unaltered and the object looks normal. At a curved surface the two faces meet the beam at a different slant at every point, so the outer rays are bent more than the inner ones — the beam is squeezed together or opened out, and the object we see is magnified or shrunk.
Check it yourself: look at this line of print through a glass tumbler full of water. Through the flat rim nothing changes; through the curved side the letters stretch.
Q2.
But would those objects continue to look the same if the surface of the transparent material is curved?
Answer
No, they would not.
Through a flat window pane every object keeps its size and shape — that is why we can use windows at all. The moment the transparent surface is curved, the letters or objects behind it look larger or smaller than they really are. Activity 10.8 shows this with nothing more than a drop of water.
Why flat glass is the special case: at a flat sheet, the ray bends on the way in and bends back by exactly the same amount on the way out, because the two faces are parallel. The ray therefore leaves travelling in its original direction — shifted a little sideways, but not turned. Curved faces are not parallel, so the two bends do not cancel, and the direction of the ray really is changed.