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# Mechanical Operations MCQ’s – Particle Size

What is Φ_{s}?

a) Sphere

b) Cubicity

c) Sphericity

d) Void age

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Answer: c

Explanation: Φ_{s} is defined as the measure of the roundness of a sphere, it is also the ratio of the surface area of same volume particle and the surface area of particle

For a spherical particle of diameter D_{p}, Φ_{s} is ____

a) 0

b) 0.5

c) 1

d) 2

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Answer: c

Explanation: As the particle is totally spherical the Sphericity is always 1, for a sphere of diameter D_{p}, Φ_{s} = 1.

For any non-spherical particle, Sphericity is defined as _____

a) 6V_{p}/D_{p}P_{s}

b) 6V_{p}/P_{s}S_{p}

c) V_{p}/D_{p}S_{p}

d) 6V_{p}/D_{p}S_{p}

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Answer: d

Explanation: Sphericity for any non-spherical particle is defined as 6V_{p}/D_{p}S_{p}, where D_{p} is the diameter and V_{p} and S_{p} are volume and surface area respectively.

For a crushed material, Φ_{s} lies between _____

a) 0.6 to 0.8

b) 1 to 2

c) 1.2 to 1.8

d) 1.6 to 1.8

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Answer: a

Explanation: As per the empirical calculations and the final results obtained from various experimental values the Φ_{s} is calculated to be between 0.6 and 0.8.

For cubes and cylinders, what is Φ_{s}?

a) 0.65 and 0.50

b) 0.81 and 0.87

c) 0.660 and 0.556

d) 13.2 and 12.3

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Answer: b

Explanation: For cubes and cylinders for which the length L equals to the diameter, equivalent diameter is greater than L, Φ_{s} would be 0.81 and 0.87.

Which of the following gives the total volume of the particles?

a) m/P_{p}

b) D_{p}/ P_{p}

c) M_{v}/P_{p}

d) M_{v}/D_{p}

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Answer: a

Explanation: The total volume of the particles is given by m/P_{p}, where m is the total mass of the sample and D_{p} is the diameter of the particle.

Which of the following gives the number of particles?

a) mV_{p}/P_{p}

b) D_{p}/ P_{p}

c) m/P_{p}V_{p}

d) M_{v}/D_{p}

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Answer: c

Explanation: The total number of the particles is given by m/P_{p}V_{p}, where m is the total mass of the sample, D_{p} is the diameter and V_{p} is the volume of particle.

Which of the following gives the total surface area of the particle?

a) N*S_{p}

b) V_{p}*S_{p}

c) S_{p}/D_{p}

d) S_{p}/V_{p}

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Answer: a

Explanation: The total surface area of the particle is given by A = N*S_{p}, where N is the number of the particles and S_{p} is the surface area of individual particle.

The two basic methods of analysis are ______

a) Cumulative and Affirmative

b) Cumulative and Frequency

c) Frequency and Affirmative

d) Affirmative and Conservative

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Answer: b

Explanation: The two basic method of analysis of screening are Cumulative and Frequency plot techniques, one uses particle size while other one uses screen size.

What is N_{P}_{r}?

a) Pradtl Number

b) Peclet Number

c) Priyang Number

d) Prag Number

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Answer: a

Explanation: The Prandtl number (Pr) is defined as the ratio of momentum diffusivity to thermal diffusivity i.e. [CPµ/K].