Question

In case of fluid flowing on horizontal surface the flow of fluid becomes unsteady when Reynolds number (Rn) is

• A. less than 499
• B. between 500 - 999
• C. between 1000 - 1999
• D. greater than 2000

Hint:

In the Std XI classification, flow is streamline below 1000, unsteady between 1000 and 2000, and turbulent above 2000.

Answer 1

The Correct Option is C

Step 1: Recall the three bands:
The textbook gives three bands of Reynolds number: below 1000 is streamline, 1000 to 2000 is unsteady (transitional), and above 2000 is turbulent.

Step 2: Place the options:
(A) below 499 and (B) 500 to 999 are both streamline. (D) above 2000 is turbulent.
(C) 1000 to 1999 matches the unsteady band.

Step 3: Why it makes sense:
As the speed rises, the viscous forces lose control. The flow first becomes erratic and then fully turbulent.

Final Answer:
Option (C). \[ \boxed{1000 < R_n < 2000 \text{ (C)}} \]