# Mechanical Operations Questions and Answers – Particle Size

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This set of Mechanical Operations Multiple Choice Questions & Answers (MCQs) focuses on “Particle Size”.

1. What is Φs?
a) Sphere
b) Cubicity
c) Sphericity
d) Void age

Explanation: Φs 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.

2. For a spherical particle of diameter Dp, Φs is ____
a) 0
b) 0.5
c) 1
d) 2

Explanation: As the particle is totally spherical the Sphericity is always 1, for a sphere of diameter Dp, Φs = 1.

3. For any non-spherical particle, Sphericity is defined as _____
a) 6Vp/DpPs
b) 6Vp/PsSp
c) Vp/DpSp
d) 6Vp/DpSp

Explanation: Sphericity for any non-spherical particle is defined as 6Vp/DpSp, where Dp is the diameter and Vp and Sp are volume and surface area respectively.
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4. For a crushed material, Φs lies between _____
a) 0.6 to 0.8
b) 1 to 2
c) 1.2 to 1.8
d) 1.6 to 1.8

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

5. For cubes and cylinders, what is Φs?
a) 0.65 and 0.50
b) 0.81 and 0.87
c) 0.660 and 0.556
d) 13.2 and 12.3

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

6. Which of the following gives the total volume of the particles?
a) m/Pp
b) Dp/ Pp
c) Mv/Pp
d) Mv/Dp

Explanation: The total volume of the particles is given by m/Pp, where m is the total mass of the sample and Dp is the diameter of the particle.

7. Which of the following gives the number of particles?
a) mVp/Pp
b) Dp/ Pp
c) m/PpVp
d) Mv/Dp

Explanation: The total number of the particles is given by m/PpVp, where m is the total mass of the sample, Dp is the diameter and Vp is the volume of particle.

8. Which of the following gives the total surface area of the particle?
a) N*Sp
b) Vp*Sp
c) Sp/Dp
d) Sp/Vp

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

9. The two basic methods of analysis are ______
a) Cumulative and Affirmative
b) Cumulative and Frequency
c) Frequency and Affirmative
d) Affirmative and Conservative

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.

10. What is NPr?
b) Peclet Number
c) Priyang Number
d) Prag Number

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

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