JEE Main · 2008 · 27 Apr 2008 · Offline · Fluid Mechanics

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A capillary tube (A) is dropped in water. Another identical tube (B) is dipped in a soap water solution. Which of the following shows the relative nature of the liquid columns in the two tubes?

(A)(see structure)
A
B
(B)(see structure)
A
B
(C)(see structure)
A
B
✓ Correct
(D)(see structure)
A
B

Answer: (C)

Solution

Capillary rise is

h = \frac{2 T c o s θ}{ρ g r}

, so for identical tubes the height rises or falls with the surface tension

T

of the liquid. A soap solution has a markedly lower surface tension than pure water, so the liquid in the soap-solution tube rises less than the water in the plain tube. The picture in which the water column stands higher than the soap-solution column is the one that represents the two tubes correctly.

JEE Main · 2008 · 27 Apr 2008 · Offline · Single correct option

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