# Food Engineering Questions and Answers – Unit Operations – Rheology of Foods

This set of Food Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Unit Operations – Rheology of Foods”.

1. Rheology of food in the food processing industry is how the food is affected when _____ is applied.
a) Pressure
b) Butter
c) None of the mentioned
d) All of the mentioned

Explanation: Rheology of food in the food processing industry is how the food is affected when Pressure is applied.

2. Statement 1: Starch is _____ as its viscosity decreases with an increase in shear stress.
Statement 2: Bingham plastics follow Newton’s law of viscosity at low shears.
a) Bingham, False
b) Dilatant, True
c) Pseudo plastic, False
d) Newtonian fluid, True

Explanation: Starch is Pseudo plastic as its viscosity decreases with an increase in shear stress. Bingham plastics follow Newton’s law of viscosity at high shears. At low shears, they’ve infinite viscosity.

3. Statement 1: Blood is a _____
Statement 2: Thixotropic fluids are fluids whose viscosity decreases when subjected to shear stress initially but eventually with time, the viscosity increases.
a) Newtonian fluid, False
b) Rheopectic, True
c) Pseudo plastic, False
d) Casson plastic, True

Explanation: Blood is a Casson plastic. At low shears, they’ve infinite viscosity. At high shears, its viscosity decreases with increase in shear. Statement 2 is true.

4. Which of the flowing is true about two-parameter model?
a) It is also called as Ostwald-de Waele Model
b) The equation pertaining to it is τ=Kγn
c) These equations pertain to Newtonian, dilatant and pseudo plastic fluids
d) All of the mentioned

Explanation: All the given statements about the two-parameter model are true.

5. Statement 1: Apparent viscosity μ_a is related to shear stress (τ) and shear strain (γ) as μ_a= τ/γ.
Statement 2: The equation τ=Kγn becomes μ_a= τ/γ = Kγ(n-1) .
a) True, False
b) True, True
c) False, False
d) False, True

Explanation: Both the statements are true.
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6. Statement 1: In μ_a= τ/γ = Kγ(n-1) , n = consistency index and K is the flow behaviour index.
Statement 2: n= 1 for Newtonian fluids, n<1 for dilatant fluids and n>1 for pseudo plastic fluids.
a) True, False
b) True, True
c) False, False
d) False, True

Explanation: Both the statements are false. K = consistency index and n is the flow behaviour index. n is greater than 1 for dilatant fluids and n is less than 1 for pseudo plastic fluids.

7. Statement 1: Considering the equation, μ_a= τ/γ = Kγ(n-1) , for pseudo plastic fluids, n<1 and they’re called Shear thinning liquids and dilatant fluids are called Shear thickening liquids as n>1.
Statement 2: Cooked starch solution is a Shear thinning liquid and dairy cream is a Shear thickening liquid.
a) True, False
b) True, True
c) False, False
d) False, True

Explanation: Statement 1 is true. But, cooked starch solution is a Shear thickening liquid and dairy cream is a Shear thinning liquid.

8. Which of the following is a name of an actual viscometer?
a) Capillary tube
b) Plate and Cone
c) Coaxial Cylinder
d) All of the mentioned

Explanation: All of the mentioned, Capillary tube, Plate and Cone and Coaxial Cylinder are all names of viscometers.

9. Statement 1: Brookfield viscometer is an example of Coaxial Cylinder Viscometer.
Statement 2: Working principle of a Brookfield viscometer: Two coaxial cylinders. Liquid is filled in between them. The viscosity produces torque which is directly proportional to the shear stress.
a) True, False
b) True, True
c) False, False
d) False, True

Explanation: Both the statements pertaining to Brookfield viscometer are true.

10. Statement 1: Brookfield viscometer is very robust, is supported by software and even shows values of K and n, but, sometimes particles suspended in the fluid cause problems.
Statement 2: Drawbacks of plate and cone viscometer: edge-effects, turbulence and temperature effects.
a) True, False
b) True, True
c) False, False
d) False, True

Explanation: Both the statements pertaining to viscometers are true.

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