Mechanical Operations

241. Rittinger's crushing law states that

1. Work required to form a particle of any size is proportional to the square of the surface to volume ratio of the product
2. Work required to form a particle of a particular size is proportional to the square root of the surface to volume ratio of the product
3. Work required in crushing is proportional to the new surface created
4. For a given machine and feed, crushing efficiency is dependent on the size of the feed & product

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242. Rittinger's number designates the new surface created per unit mechanical energy absorbed by the material being crushed. Larger value of Rittinger's number of a material indicates its

1. Easier grindability
2. Poor grindability
3. High power consumption in grinding
4. None of these

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243. Rod mills employed for grinding

1. Employ a steel shell having L/D ratio of 1.5 to 3.0
2. Is useful for handling sticky materials
3. Employ steel rods of 2-12 cms diameter extending over full length of the mill
4. All 'a', 'b' & 'c'

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244. rpm of a trommel at critical speed is given by (where, D = Diameter of trommel in ft)

1. 76.65/D
2. 76.65/√D
3. 76.65/D²
4. 76.75 √D

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245. Run of mine (ROM) coal is crushed by a _________ for use in domestic ovens.

1. Jaw crusher
2. Hammer crusher
3. Ball mill
4. Tube mill

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246. Sauter mean diameter is the same as the _________ mean diameter.

1. Mass
2. Arithmetic
3. Volume-surface
4. Geometric

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247. Screen capacity is expressed in terms of

1. tons/hr
2. tons/ft2
3. Both (A) & (B)
4. tons/hr-ft2

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248. Screen capacity is not a function of

1. Its openings size
2. Screening mechanism
3. Screening surface
4. Atmospheric humidity

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249. Screen capacity is proportional to (where, S = screen aperture)

1. S
2. 1/S
3. S²
4. √S

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250. Screen efficiency is

1. Recovery/rejection
2. Recovery
3. Rejection
4. None of these

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