In Indian Standard (IS) test sieves used for particle-size analysis, the “mesh number” is defined as the aperture size expressed to the nearest decamicron (0.01 mm). Approximately how many micrometres is the aperture width for an IS sieve of mesh.

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Introduction / Context:IS (Indian Standard) sieves are widely used in chemical engineering and materials processing for particle size classification. This question checks your understanding of the definition of IS “mesh number” and how to convert it into a practical aperture size in micrometres for calculations or lab work. Given Data / Assumptions: IS mesh number is equal to the aperture size expressed to the nearest decamicron. 1 decamicron = 0.01 mm = 10 micrometres. Required: aperture for mesh number 50 in micrometres. Concept / Approach:The mapping is direct: mesh number = aperture (in decamicrons). Convert decamicrons to millimetres and then to micrometres. Remember 1 mm = 1000 micrometres. This avoids confusion with “mesh per inch,” which is a different convention used in ASTM/BS standards. Step-by-Step Solution: Step 1: Interpret “mesh number 50” as 50 decamicrons.Step 2: Convert decamicrons to millimetres: 50 decamicrons * 0.01 mm/decamicron = 0.50 mm.Step 3: Convert millimetres to micrometres: 0.50 mm * 1000 μm/mm = 500 μm. Verification / Alternative check:If the sieve were specified by “openings per inch,” the number would not match this value. Because the question explicitly uses the IS definition (aperture expressed in decamicrons), the direct conversion to 0.50 mm (500 μm) is correct. Why Other Options Are Wrong: 5 μm and 50 μm are far too fine for a 50-decami﻿cron IS aperture (which equates to 0.50 mm).5000 μm = 5 mm is much coarser than typical lab sieves near this designation.250 μm corresponds to mesh number 25 under the IS decamicron convention, not 50. Common Pitfalls:Confusing IS “mesh number” with “mesh per inch”; omitting the conversion 1 mm = 1000 μm; or misreading decamicron as micrometre can all lead to errors by a factor of 10 or 20. Final Answer:500

In Indian Standard (IS) test sieves used for particle-size analysis, the “mesh number” is defined as the aperture size expressed to the nearest decamicron (0.01 mm). Approximately how many micrometres is the aperture width for an IS sieve of mesh number 50?

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