Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Energy dissipation in hydraulic jump is mainly by the large eddies in turbulence.
Reason (R): Large eddies transport the fluid over large distance, thus causing the mixing effect of turbulence.
In the light of the above statements, choose the most appropriate answer from the options given below:

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

The efficiency of a hydraulic jump is the ratio of energy after the jump to energy before it. Higher Froude numbers ($F_r$) result in more energy dissipation and stronger eddies.

Answer 1

The Correct Option is A

Concept: A hydraulic jump is an extremely turbulent phenomenon where kinetic energy is converted into potential energy and thermal energy (heat).

Step 1: Analyze energy dissipation in the jump.
The sudden transition from supercritical to subcritical flow creates a violent "roller" or "eddy" zone. This high-intensity turbulence is the primary mechanism for the loss of mechanical energy. Thus, Assertion (A) is correct.

Step 2: Analyze the role of eddies.
Turbulence consists of eddies of various sizes. The largest eddies are responsible for the bulk transport and mixing of the fluid, which facilitates the rapid conversion of organized kinetic energy into disorganized turbulent energy, eventually dissipating as heat through smaller eddies. Thus, Reason (R) is correct.

Step 3: Establish the connection.
The mixing and transport provided by the large eddies (R) is exactly what causes the energy dissipation mentioned in (A).