Question:

Two reservoirs at different levels are connected by two parallel pipes of diameter \(2d\) and \(d\). The ratio of the flows in the larger to smaller pipe is

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For parallel pipes having equal head loss, \[ \boxed{ Q\propto D^{5/2} } \] Thus, \[ \boxed{ \frac{Q_1}{Q_2} = \left(\frac{D_1}{D_2}\right)^{5/2}. } \]
Updated On: Jul 23, 2026
  • \(\sqrt{2}:1\)
  • \(2:1\)
  • \(4:1\)
  • \(4\sqrt{2}:1\)
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The Correct Option is D

Solution and Explanation

Concept: For two parallel pipes connecting the same reservoirs, the head loss in each pipe is the same. Using Darcy-Weisbach equation, \[ h_f\propto\frac{Q^2}{D^5} \] Since the head losses are equal, \[ \frac{Q_1^2}{D_1^5} = \frac{Q_2^2}{D_2^5}. \] Therefore, \[ \boxed{ \frac{Q_1}{Q_2} = \left(\frac{D_1}{D_2}\right)^{5/2} } \]

Step 1:
Write the given diameters. \[ D_1=2d, \] \[ D_2=d. \]

Step 2:
Calculate the discharge ratio. \[ \frac{Q_1}{Q_2} = \left(\frac{2d}{d}\right)^{5/2} = 2^{5/2} = 4\sqrt2. \] Hence, \[ \boxed{ Q_1:Q_2 = 4\sqrt2:1. } \] Therefore, the correct option is \[ \boxed{(D)\;4\sqrt2:1.} \]
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