GATE 2019 CE (CE1) – Question 30
A completely mixed dilute suspension of sand particles of diameters 0.25, 0.35, 0.40, 0.45 and 0.50 mm fills a transparent glass column 10 cm in diameter and 2.50 m high. It settles undisturbed; all 0.35 mm particles reach the bottom in 30 s. For the same 30 s, find percentage removal of 0.45 and 0.50 mm particles, to the nearest integer.
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Correct answer: 100 to 100
Explanation
For otherwise identical particles, settling speed increases with diameter. Even the 0.35 mm particles starting at the column top reach the bottom within 30 s. The larger 0.45 and 0.50 mm particles therefore also settle completely: **100% removal** for each class.