NCERT Solutions Curiosity Chapter 9 –167Winnowing indoors, and sieving the atta — In-text Questions
Book page 166 Updated on2026-09-05
Q1.
Valli is unable to separate husk from rice in a closed room. How can you help her?
Answer
Winnowing needs moving air. A closed room has none, so nothing gets carried away. Give Valli one of these:
Switch on a fan — a table fan or the ceiling fan on low speed — and let her drop the mixture slowly in front of it. The husk is blown aside.
Blow on it herself, exactly as in Activity 9.1 with the peanut skins, taking a little of the mixture at a time on a plate.
Open a window or door and stand in the draught, or step out into the courtyard where a breeze is blowing.
Sieve it if the husk pieces are much bigger than the rice grains — that uses size instead of weight and does not need air at all.
Why the fan works: winnowing does not really need wind — it needs air moving past the falling mixture. A fan makes exactly that. The husk, being lighter, is pushed sideways; the rice, being heavier, falls into the tray.
Check it yourself: Hold a plate of poha and a few grains of rice in front of a table fan. Notice how much further the poha travels. Same wind, different weights — different landing places.
Q2.
Carefully observe a sieve. Are all the holes of the sieve the same size? Will sieving work if the holes of the sieve are larger than the substances? Is there any difference in the size between the particles that pass through the sieve and the particles that remain on the sieve?
Answer
Taking the three questions one by one:
Are all the holes the same size? — Yes. In one sieve every hole is of the same size, and they are evenly spaced. That is what makes the sieve a fair “size test”: a particle either fits through every hole or through none of them.
Will sieving work if the holes are larger than the substances? — No. If both components are smaller than the holes, everything falls through and nothing is separated. Sieving works only when the hole size lies between the sizes of the two components.
Is there a difference in size between what passes and what stays? — Yes, and that is the whole point. Whatever comes through is smaller than a hole; whatever stays back is bigger than a hole.
Fine atta particles < hole size → pass through (this is the flour we use)
Bran and small stones > hole size → remain on the sieve
Why the right sieve matters: a sieve does not ask what a thing is made of, only how big it is. So the whole job is choosing a sieve whose holes are bigger than the component you want to collect below and smaller than the component you want to hold back. A tea strainer will not sift flour, and a flour chalni will not strain tea.
Tip: Sieving is used only for a solid–solid mixture whose particles differ in size. It cannot separate two solids of the same size, and it cannot pull a dissolved solid out of water.
Q3.
Have you ever observed sieves being used at construction sites to separate pebbles and stones from the sand?
Answer
Yes. At any building site you will see a large sloping wire-mesh screen leaning against a wall. A worker throws shovelfuls of sand at it.
What happens
Why
Fine sand passes through the mesh and piles up behind it
Sand grains are smaller than the holes of the mesh
Pebbles, stones and lumps slide down the face of the mesh and collect in front
They are bigger than the holes, so they cannot get through
Why builders bother: plaster and mortar must be smooth. A single pebble in the mix leaves a bump or a hollow in the wall. The clean sieved sand goes into plaster; the pebbles are not thrown away — they are used in concrete, where big pieces are wanted.
Look around: the same idea appears in a chalni for atta, the perforated basket in which vegetables are washed, a tea strainer, and the jhara used to lift pakoras out of hot oil.