Q1: Pulverised coal passing through 200 mesh screen has a diameter of 0.074 mm (74 micron). The same passing through 50 mesh screen will have a dia of __________ mm.

ANS:B - 0.30

Mesh size refers to the number of openings per inch in a screen. The diameter of particles passing through a specific mesh can be approximated using the relationship between mesh size and particle size. The mesh size (N) and the particle diameter (d) are related by the following approximate formula for standard screens: d≈25.4 mmNd \approx \frac{25.4 \text{ mm}}{N}d≈N25.4 mm​ Given:

• 200 mesh screen corresponds to a particle diameter of 0.074 mm.
• We need to find the particle diameter for a 50 mesh screen.

Using the formula: d50 mesh≈25.4 mm50=0.508 mmd_{50 \text{ mesh}} \approx \frac{25.4 \text{ mm}}{50} = 0.508 \text{ mm}d50 mesh​≈5025.4 mm​=0.508 mm However, none of the provided options directly match this result. Let's verify by considering the provided options and a possible error or different understanding of standard meshes. Given the options:

1. 0.007 mm
2. 0.30 mm
3. 50 mm
4. 0.014 mm

Clearly, 50 mm and 0.007 mm are unreasonable given the context. Between 0.30 mm and 0.014 mm, 0.30 mm is much closer to the expected value derived from the formula, though it is slightly off. Based on standard practices and common approximations: Particle diameter≈0.3 mm\text{Particle diameter} \approx 0.3 \text{ mm}Particle diameter≈0.3 mm Thus, the most reasonable and closest answer from the given options is 0.30 mm.