Mechanical Operations

271. Size reduction of the _________ can be suitably done by ball mills, crushing rolls and rod mills.

1. Metalliferous ores
2. Non-metallic ores
3. Basic slags
4. Asbestos & mica

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272. Sizing of very fine particles of the order of 5 to 10 microns is done by elutriation, which is a _________ operation.

1. Clarification
2. Sedimentation
3. Flocculation
4. Classification

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273. Soft & non-abrasive materials can be made into fines by

1. Attrition
2. Compression
3. Cutting
4. None of these

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274. Solid particles of different densities are separated by

1. Filters
2. Thickness
3. Cyclones
4. Sorting classifier

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275. Solid particles separation based on the difference in their flow velocities through fluids is termed as the

1. Clarification
2. Classification
3. Elutriation
4. Sedimentation

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276. Sorting classifiers employing differential settling methods for separation of particles make use of the differences in their

1. Particle sizes
2. Densities
3. Terminal velocities
4. None of these

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277. Specific surface area is the surface area of a unit _________ of materials.

1. Weight
2. Volume
3. Either (A) or (B)
4. Neither (A) nor (B)

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278. Sphericity for a non-spherical particle is given by (where, V and S are volume and surface area respectively of one particle. and, D = equivalent diameter of particle).

1. 6.V/D.S
2. V/6D.S
3. D.S/V
4. V/D.S

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279. Sphericity is the ratio of the surface area of a spherical particle having the same volume as the particle to the surface area of the particle. Which of the following has the maximum value of sphericity?

1. Sphere
2. Cube
3. Cylinder (L/D = 1)
4. Raschig rings

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280. Sphericity of a cubical particle, when its equivalent diameter is taken as the height of the cube, is

1. 0.5
2. 1
3. √2
4. √3

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