Engineering Questions with Answers - Multiple Choice Questions

# MCQs on Centrifugation

1 - Question

The centrifugation is based on the principle of when a force is less than the gravity desired.
a) True
b) False

Explanation: The “fictitious” force on everything that points opposite that of gravity, the effect of gravity is reduced. Many particles or cells in a liquid suspension, given time, will eventually settle at the bottom of a container due to gravity. However, the length of time required for such separations is impractical. Other particles, extremely small in size, will not separate at all in solution unless subjected to high centrifugal force.

2 - Question

In 500 × g, what does g represent in accordance to centrifugation?
a) Gravitational force
b) Centrifugal force is 500 times greater than earthly gravitational force
c) Centrifugal force is 500 times less than earthly gravitational force
d) Centrifugal force is 500 times same as that of earthly gravitational force

Explanation: Centrifuge is any device that applies a sustained centrifugal force; that is, a force due to rotation. Effectively, the centrifuge substitutes a similar, stronger, force for that of gravity.
When a suspension is rotated at a certain speed or revolutions per minute (RPM), centrifugal force causes the particles to move radially away from the axis of rotation. The force on the particles (compared to gravity) is called Relative Centrifugal Force (RCF). For example, an RCF of 500 x g indicates that the centrifugal force is 500 times greater than earthly gravitational force.

3 - Question

Which of the following is not a type of centrifugation?
a) Hydro cyclone
b) Tubular centrifuge
c) Microfiltration
d) Disk stack separator

Explanation: Microfiltration is a membrane filtration process which removes contaminants from a fluid by microporous membrane. The membrane pore size ranges from 0.1 to 10 micrometers. Microfiltration is different from reverse osmosis and nanofiltration because it does not require pressure and does not remove dissolved contaminants. However, centrifugation is often effective when the particles are very small and difficult to filter.

4 - Question

. By increasing the feed rate of the liquid in tubular centrifuge the performance is increased.
a) True
b) False

Explanation: As the feed rate is increased the liquid layer moving up the wall of the centrifuge becomes thicker; this reduces the performance of the centrifuge by increasing the distance a particle must travel to reach the wall. Liquid from the feed spills over a weir at the top of the bowl. When the thickness of sediment collecting in the bowl reaches the position of the liquid-overflow weir, separation efficiency declines rapidly. This limits the capacity of the centrifuge.

5 - Question

. At what speed do you centrifuge blood?
a) 2200-2500 RPM
b) 3000-3200 RPM
c) 1000-1500 RPM
d) 4000 RPM

Explanation: Do not centrifuge immediately after drawing blood. Allow the blood to clot in an upright position for at least 30 minutes but not longer than 1 hour before centrifugation. Perform venipuncture as with any other blood collection device. Centrifuge for at least 15 minutes at 2200-2500 RPM within one hour of collection.

6 - Question

Which of the following centrifugation is used to separate certain organelles from whole cell?
a) Rate-zonal centrifugation
b) Normal centrifugation
c) Differential centrifugation
d) Isopycnic centrifugation

Explanation: The simplest form of separation by centrifugation is differential centrifugation, sometimes called differential pelleting. Particles of different densities or sizes in a suspension will sediment at different rates, with the larger and denser particles sedimenting faster. These sedimentation rates can be increased by using centrifugal force. A suspension of cells subjected to a series of increasing centrifugal force cycles will yield a series of pellets containing cells of decreasing sedimentation rate.
Differential centrifugation is a common procedure in microbiology and cytology used to separate certain organelles from whole cells for further analysis of specific parts of cells.

7 - Question

. A viscous solution contains particles with a density is to be clarified by centrifugation. The solution density is and its viscosity is 80 cp. The centrifuge has a bowl with and 3 1200 / p ρ = kg m3 ρ = 850 / kg m2r m = 0.02 1 r = 0.01 m and height b=0.25 m. Calculate the critical particle diameter of the largest particles in the exit stream if N=15000 rpm and flow rate q=0.002 m3 /hr?
a) 2.9 μm
b) 2.66 μm
c) 3.15 μm
d) 2.57 μm

8 - Question

. Which of the following is used as a media for density gradient?
a) Agarose
b) Ficoll
c) Luria broth
d) Propylene glycol

Explanation: Ficoll is a neutral, highly branched, high-mass, hydrophilic polysaccharide which dissolves readily in aqueous solutions. Ficoll is part of Ficoll-Paque, which is used in biology laboratories to separate blood to its components (erythrocytes, leukocytes, etc.). Ficoll-Paque is normally placed at the bottom of a conical tube, and blood is then slowly layered above Ficoll-Paque.

9 - Question

. From the following which is the type of filtration centrifuge?
a) Screen/scroll centrifuge
b) Tubular centrifuge
c) Decanter centrifuge
d) Separator centrifuge

Explanation: For the filtration or the so-called screen centrifuge the drum is perforated and is inserted with a filter, for example a filter cloth, wire mesh or lot screen. The suspension flows through the filter and the drum with the perforated wall from the inside to the outside. In this way, the solid material is restrained and can be removed. The kind of removing depends on the type of centrifuge, for example manually or periodically.

10 - Question

Which of the following is used in uranium enrichment?
a) Tubular centrifuge
b) Disk-stack centrifuge
c) Gas centrifuge
d) Zippe-type centrifuge

Explanation: Gas centrifuges are used in uranium enrichment. The heavier isotope of uranium (uranium-238) in the uranium hexafluoride gas tends to concentrate at the walls of the centrifuge as it spins, while the desired uranium-235 isotope is extracted and concentrated with a scoop selectively placed inside the centrifuge. It takes many thousands of centrifugations to enrich uranium enough for use in a nuclear reactor (around 3.5% enrichment), and many thousands more to enrich it to weapons-grade (above 90% enrichment) for use in nuclear weapons.

11 - Question

What is the applied centrifugal field at a point equivalent to 5 cm from the centre of rotation and an angular velocity of 3000 rad s-1?
a) 4.5 × 10-7 cm s-2
b) 5.4 × 10-7 cm s-2
c) 3.4 × 10-7 cm s-2
d) 6.5 × 10-7 cm s-2

Explanation: The centrifugal field G, at a point 5 cm from the centre of rotation may be calculated using the equation G = ω2 r,
G = (3000)2 × 5 cm s-2 = 4.5 × 10-7 cm s-2.

12 - Question

For the pelleting of the microsomal fraction from a liver homogenate, an ultracentrifuge is operated at a speed of 40000 rpm. What is the angular velocity, ω, in radians per second?

Explanation: The angular velocity, ω, may be calculated using the equation:
ω = (2 π rev min-1)/60
ω = 2 × 3.1416 × 40000/60 rad s-1

13 - Question

What is rate-zonal centrifugation?
a) Based on separation of particles by mass
b) Based on separation of particles by density
c) Based on separation of particles on solubility
d) Based on separation of particles on size