Question

Assertion (A) For the flow to be streamlined, value of critical velocity should be as low as possible.

Reason (R) Once the actual velocity of flow of liquid becomes greater than the critical velocity, the flow becomes turbulent. (NCERT Pg. 187)

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

Answer 1

Answer: (D)

Assertion (A) is false but Reason (R) is true

Answer 2

Analysis of Assertion (A):

The assertion states, "For the flow to be streamlined, value of critical velocity should be as low as possible."

Streamlined (laminar) flow occurs when the actual velocity of the fluid is less than the critical velocity ($v < v_c$). Turbulent flow occurs when the actual velocity exceeds the critical velocity ($v > v_c$).

If the critical velocity ($v_c$) is low, it means that the flow will become turbulent at a relatively low actual velocity. This implies that the range of velocities for which the flow remains streamlined is small.

For a flow to be streamlined and to remain streamlined over a wider range of actual velocities, the critical velocity should be high, not low. A high critical velocity allows the flow to maintain its laminar nature even at higher speeds. Therefore, the assertion is false.

Analysis of Reason (R):

The reason states, "Once the actual velocity of flow of liquid becomes greater than the critical velocity, the flow becomes turbulent."

This is the fundamental definition of critical velocity and the condition for the transition from laminar to turbulent flow. When the fluid's actual velocity exceeds its critical velocity, the flow pattern changes from orderly (streamlined) to disorderly (turbulent). This statement is true.

Conclusion:

Assertion (A) is false, and Reason (R) is true.