Question

Three capillaries of same length but radii 2r, 3r,4r are connected in series and a liquid flows through them in stream line flow. If the pressure across the third capillary is 16 mm of Hg the pressure across the first capillary will be ( in mm of Hg):

• A. 25.6
• B. 2.56
• C. 256
• D. 2560

Answer 1

The correct option is C 256

flow through each section will be same.

$V=\frac{\pi P_1(2r{)}^4}{8\eta l}$....(1)

$V=\frac{\pi P_2(3r{)}^4}{8\eta l}$.....(2)

$V=\frac{\pi P_3(4r{)}^4}{8\eta l}$.....(3)

from above three equation

$16P_1=256P_3,P_3=16$

$P_1=256$ mm of Hg