Sieving
Sometimes, mixtures contain components that are of different sizes. Handpicking takes too long, and winnowing won’t work if both components are heavy. In such cases, we use a sieve.
Definition: Sieving is the process of separating solids from a mixture based on variations in particle size using a sieve (a mesh or net).
How it Works
A sieve has small holes (pores).
- Smaller particles pass through the holes.
- Larger particles (impurities) remain on the sieve.
Common Examples
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In the Kitchen (Flour):
- We sieve wheat flour to remove bran and small impurities that might have remained after grinding. The fine flour passes through, while the bran stays on top.
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At Construction Sites (Sand):
- Large sieves are used to separate pebbles and stones from sand. Fine sand is needed for mixing cement, while stones would ruin the smooth finish.
Diagram: The Sieve Concept
Warning
Think: If you try to sieve a mixture of rice and kidney beans (rajma) using a sieve with very large holes, both will fall through. The pore size of the sieve determines what gets separated!