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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Some Mechanical Properties of Matter

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Some Mechanical Properties of Matter

A capillary tube with a radius of 0.50 mm is vertically dipped into...

A capillary tube with a radius of 0.50 mm0.50 \text{ mm} is vertically dipped into a pot of water. Find the difference between the pressure of the water inside the tube 5.0 cm5.0 \text{ cm} below the surface and the atmospheric pressure. The surface tension of water is 0.075 N/m0.075 \text{ N/m}.

Options

  1. A490 N/m2490 \text{ N/m}^2
  2. B190 N/m2190 \text{ N/m}^2
  3. C300 N/m2300 \text{ N/m}^2
  4. D790 N/m2790 \text{ N/m}^2

Correct answer

B. 190 N/m2190 \text{ N/m}^2

Step-by-step solution

The pressure just below the meniscus in the capillary tube is given by P0−2TrP_0 - \dfrac{2T}{r}, where P0P_0 is the atmospheric pressure, TT is the surface tension, and rr is the radius of the tube.

The pressure PP at a depth hh below the meniscus inside the tube is:

P=P0−2Tr+ρghP = P_0 - \dfrac{2T}{r} + \rho g h

The difference between this pressure and the atmospheric pressure is:

ΔP=P−P0=ρgh−2Tr\Delta P = P - P_0 = \rho g h - \dfrac{2T}{r}

Given values are:

ρ=1000 kg/m3\rho = 1000 \text{ kg/m}^3

g=9.8 m/s2g = 9.8 \text{ m/s}^2

h=5.0 cm=0.05 mh = 5.0 \text{ cm} = 0.05 \text{ m}

T=0.075 N/mT = 0.075 \text{ N/m}

r=0.50 mm=0.5×10−3 mr = 0.50 \text{ mm} = 0.5 \times 10^{-3} \text{ m}

Calculating the hydrostatic pressure term:

ρgh=1000×9.8×0.05=490 N/m2\rho g h = 1000 \times 9.8 \times 0.05 = 490 \text{ N/m}^2

Calculating the capillary pressure term:

2Tr=2×0.0750.5×10−3=300 N/m2\dfrac{2T}{r} = \dfrac{2 \times 0.075}{0.5 \times 10^{-3}} = 300 \text{ N/m}^2

Substituting these values into the pressure difference equation:

ΔP=490−300=190 N/m2\Delta P = 490 - 300 = 190 \text{ N/m}^2
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