# Food Processing Unit Operations Questions and Answers – Filtering Medium Resistance

This set of Food Processing Unit Operations Multiple Choice Questions & Answers (MCQs) focuses on “Filtering Medium Resistance”.

1. What is the pore size in nano filtration?
a) 1-10 nanometers
b) 10-50 nanometers
c) 50-100 nanometers
d) 100-150 nanometers

Explanation: Nano-filtration is a membrane filtration based method that uses nanometer sized through pores that pass through the membrane. These membranes have pore sizes from 1-10 nanometers.

2. What is the pore size in micro filtration?
a) Around 0.1 micron
b) Around 0.01 micron
c) Around 0.001 micron
d) Around 0.0001 micron

Explanation: A microfiltration filter has a pore size around 0.1 microns, so therefore when water undergoes microfiltration, microorganisms are removed, but viruses remain in the water.

3. What is the pore size in ultra-filtration?
a) Around 0.1 micron
b) Around 0.01 micron
c) Around 0.001 micron
d) Around 0.0001 micron

Explanation: An ultrafiltration filter has a pore size around 0.01 microns. Ultrafiltration would remove larger particles and also remove some viruses. It is a membrane filtration process where hydrostatic pressure forces a liquid against a semi permeable membrane.

4. What is the pore size in membrane filter?
a) 0.12–0.25 μm
b) 0.22–0.45 μm
c) 0.32–0.55 μm
d) 0.52–0.65 μm

Explanation: Membrane filter has the pore size of 0.22–0.45 µm with thickness 150 µm, restricts the passing through activity of Pseudomonas aeruginosa and other bacterial species.

5. Which of the following statements about ultra-filtration are correct?
Statement 1: Hydrostatic pressure forces a liquid against a semi permeable membrane.
Statement 2: High molecular weight is retained.
a) True, False
b) True, True
c) False, True
d) False, False

Explanation: In ultrafiltration, hydrostatic pressure forces liquid against a semi permeable membrane. Suspended solids and solutes of high molecular weight are retained whereas the water and low molecular weight solutes pass over the membrane.
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6. What is filtration medium resistance?
a) Resistance by cake
b) Resistance by filter medium
c) Resistance by solution
d) Resistance by cake and filter medium

Explanation: The filter medium resistance is the resistance due to the solid particles which forms the cake and also the filter medium. It has the meaning of the measure of the average ability of solid particles to pass through a filter medium.

7. Which principle is behind filtration medium resistance?
a) Darcy’s law
b) Henry’s law
c) Dalton’s law
d) Newton’s law

Explanation: Darcy’s law is used to determine the specific cake resistance and filtration medium resistance from the filtration. It is an equation that defines the ability of a fluid to flow through a porous media.

8. What controls the filtration medium resistance?
a) Pressure drop alone
b) Flow rate alone
c) Both pressure drop and flow rate
d) Cake thickness

Explanation: Both pressure drop and flow rate controls the resistance due to the solid particles which forms the cake and also the filter medium. It also resists the influence of the force due to pressure difference across the filter medium.

9. How does filter medium resist?
a) Due to pressure difference
b) Due to temperature difference
c) Due to concentration difference
d) Due to concentration and temperature difference

Explanation: In filtration, the filter medium also resists along with filter cake under the influence of theforce due to pressure difference across the filter medium.

10. Which of the following statements about filtration medium resistance are correct?
Statement 1: Filtration resistance results in frictional drag.
Statement 2: Filtrate velocity is directly proportional to pressure difference.
a) True, False
b) True, True
c) False, True
d) False, False

Explanation: Filtration resistance due to cake and filtrate medium results in frictional drag on the liquid as it passes through the cake and medium. Filtrate velocity is directly proportional to pressure difference forced over cake and medium.

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