Hydraulics And Fluid Mechanics MCQ Questions & Answers | Civil Engineering

Viscosity is a measure of a fluid's resistance to flow. It is affected by temperature differently for liquids and gases.

Effect of Temperature on Liquids:

- As temperature increases, the kinetic energy of liquid molecules increases.

This weakens intermolecular forces, making it easier for the liquid to flow.
As a result, the viscosity of a liquid decreases with an increase in temperature.


Effect of Temperature on Gases:

- In gases, viscosity is primarily due to the momentum transfer between molecules.

As temperature increases, the molecular collisions increase, leading to higher viscosity.

Analysis of Options:

- Option A: Increase in viscosity of gas → Correct for gases, but the question focuses on general fluid behavior.

Option B: Increase in viscosity of liquid → Incorrect, as liquid viscosity decreases with temperature.
Option C: Decrease in viscosity of gas → Incorrect, as gas viscosity increases with temperature.
Option D: Decrease in viscosity of liquid → Correct, as liquid viscosity reduces when temperature rises.



Conclusion: The correct answer is Option D: decrease in viscosity of liquid because higher temperatures reduce intermolecular forces in liquids, allowing them to flow more easily.

Surface tension is indeed a measure of the energy required to increase the surface area of a liquid by a unit amount, and it is commonly expressed in units of energy per unit area (such as N/m or dyn/cm). Option B (distance) is not correct, and option C (both of the above) is not accurate in this context. So, for the specific field of Hydraulics and Fluid Mechanics, the correct answer is option A.

We know that Surface Tension (σ) = Force / Length

Step-by-Step Dimensional Analysis:

1. Dimensional Formula of Force (F):
- Force = Mass × Acceleration
- Acceleration = Length / Time² = LT^-2
- So, Force = M × LT^-2 = MLT^-2

2. Dimensional Formula of Length (L):
- L = L¹

3. Dividing Force by Length:
- σ = (MLT^-2) / L
- σ = ML^(1-1)T^-2 = ML⁰T^-2

Thus, the correct dimensional formula for surface tension is ML⁰T^-2, making Option B the correct choice.

Bernoulli's theorem states that in an ideal fluid flow, the sum of pressure energy, kinetic energy, and potential energy per unit volume remains constant along any streamline. This principle can be applied to various types of flow measurement devices to determine the flow rate of a fluid. The instruments mentioned in the options are commonly used to measure flow based on Bernoulli's theorem.

Venturimeter: A venturimeter is a device used to measure the flow rate of a fluid in a pipe by utilizing the principle of Bernoulli's theorem. It consists of a converging section followed by a throat and then a diverging section. The pressure difference between the converging and diverging sections is used to determine the flow rate.
Orifice Plate: An orifice plate is another flow measurement device based on Bernoulli's theorem. It consists of a thin plate with a hole (orifice) in it, placed in the pipeline. The pressure difference across the orifice is used to calculate the flow rate.
Pitot Tube: A pitot tube is used to measure fluid velocity based on Bernoulli's theorem. It has a pointed end that faces the fluid flow, and a pressure difference is created between the pointed end and the open end of the tube, which is used to determine the fluid velocity.

All of the above instruments (Venturimeter, Orifice Plate, and Pitot Tube) are utilized to measure flow by applying Bernoulli's theorem. They exploit the relationship between fluid pressure, velocity, and elevation to determine the flow rate accurately.

Therefore, the correct answer is Option D: all of the above.