An incompressible liquid is kept in a container having a weightless piston with a hole. A capillary tube of…

An incompressible liquid is kept in a container having a weightless piston with a hole. A capillary tube of inner radius 0.1 mm is dipped vertically into the liquid through the airtight piston hole, as shown in the figure. The air in the container is isothermally compressed from its original volume V0 to 100101V0 with the movable piston. Considering air as an ideal gas, the height h of the liquid column in the capillary above the liquid level in cm is _____.

[Given: Surface tension of the liquid is 0.075 N m1, atmospheric pressure is 105 N m2, acceleration due to gravity g is 10 m s2, density of the liquid is 103 kg m3 and contact angle of capillary surface with the liquid is zero]

Solution

Let Pf be the air pressure.

As the process is isothermal, we can write

P0V0=PfVf

P0V0=Pf100101V0

Pf=101×103 Pa           P0=105 N m-2

Now, consider the 4 points shown in diagram

Pd-Pc=2TR           Pd=P0

 Pc=P0-2TR

Now,

Pa=Pb (also, Pa=Pf)

Pf=ρgh+Pc

101×103=103×10×h+105-2×0.0750.1×10-3

h=14 m=25 cm

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Asked in: JEE Advanced 2023 (Paper 2)

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