NCERT Solutions Curiosity Chapter 1 Thinking like a scientist — In-text Questions
Book page 6 Updated on2026-09-05
Q1.
Have you noticed how a puri or a batura puffs up when placed in hot oil? Or how a phulka swells when put directly on the flame. Why does it puff up like a balloon? And why is one side thinner than the other?
Answer
It puffs because water inside the dough turns to steam faster than the steam can escape. A sealed crust forms on the outside within seconds, the steam trapped under it has nowhere to go, and the soft dough gives way and balloons out.
The three stages of a puri puffing. Nothing is added to the puri — the balloon is made of the puri’s own water, turned into steam.
Step by step:
Oil at about 180 °C is far above the boiling point of water, so the surface of the disc loses its water and stiffens almost at once into a thin, sealed crust.
Under the crust the water flashes into steam. As steam the same water needs more than a thousand times the room, so the pressure inside rises very fast.
The dough underneath is still soft and stretchy. Instead of tearing, it splits along the middle into two layers and balloons out — exactly like blowing into a balloon, except the blowing is done from inside.
Fried a little longer, both layers set hard and the shape holds.
And the thin side? The face that touched the oil first sets first, so it can barely stretch. The other face is still soft when the pressure arrives, so it does all the stretching — and the same dough spread over a bigger area is thinner. (See Probe and ponder Q1 for the full picture.)
Why it happens: a phulka on an open flame works the same way — the flame dries and seals the surface, the moisture inside becomes steam and blows it up. And notice what happens on your plate: the puri sags after a few minutes. The steam has cooled, condensed back into liquid water, and the pressure holding the balloon open is gone.
Tip: this also explains why cold or dry dough puffs badly. Less water inside means less steam, and less steam means less pressure to lift the layers apart.
Q2.
What are the different things that may change the way a puri puffs up when fried?
Answer
Sort them into two lists — what you can change or control, and what you can observe or measure. That single step turns a vague curiosity into an experiment, and it is exactly what the chapter asks you to do.
What we can change or control
What we can observe or measure
Thickness of the rolled dough
Did it puff up at all? (yes / no)
Size (diameter) of the rolled disc
Time taken to puff (seconds)
Type of flour — atta, maida, and so on
Does a very thick disc still give one thin side?
Temperature of the oil — boiling hot, hot, not very hot
How far it puffs — fully round, half, not at all
How the disc is put in — dropped vertically, slid at an angle, slid slowly
Did the oil splatter, smell or smoke?
How much water the dough was kneaded with; how long it rested
Colour, and whether the puri stays puffed on the plate
The rule that makes the whole thing work: change only one of these at a time and keep every other condition the same. If you want to compare boiling hot, hot and not-very-hot oil, then use discs of the same thickness, of the same flour, put in the same way. Otherwise, when a puri fails to puff, you will have no idea which of your changes was responsible.
A systematic investigation. The last box is the important one — a good experiment ends with better questions than it began with.
Why it happens: when two conditions change together you cannot tell which one caused the result — the two effects are mixed and cannot be separated afterwards. Holding everything else steady is not fussiness; it is the only way an experiment can give an answer you are entitled to trust.
Tip: not every observation is a number. “Did it puff — yes or no?” is a perfectly good scientific observation, and so is “the oil smelt burnt”. Record both kinds.