Question

The lower end of a capillary tube of radius $$2.00\,mm$$   is dipped $$10.00\,cm$$   below the surface of water in a beaker. Calculate the pressure within a bubble blown at its end in water, in excess of atmospheric pressure.
[Surface tension of water $$72 \times {10^{ - 3}}\,N/m$$   ]

A. $$718\,N{m^{ - 2}}$$
B. $$912\,N{m^{ - 2}}$$
C. $$1160\,N{m^{ - 2}}$$
D. $$1052\,N{m^{ - 2}}$$  
Answer :   $$1052\,N{m^{ - 2}}$$
Solution :
The pressure at a point just outside the bubble
$$\eqalign{ & {p_0} = {P_{{\text{atm}}}} + h\rho g = {P_{{\text{atm}}}} + 10 \times {10^{ - 2}} \times {10^3} \times 9.8 \cr & = {P_{{\text{atm}}}} + 980\,N{m^{ - 2}} \cr} $$
Now excess pressure within the bubble compared to a point just outside
$$ = \frac{{2T}}{R} = \frac{{2 \times 72 \times {{10}^{ - 3}}}}{{2 \times {{10}^{ - 3}}}} = 72\,N{m^{ - 2}}$$
$$\therefore $$ Inside pressure = excess pressure + outside pressure
$$\eqalign{ & = {P_{{\text{atm}}}} + 980 + 72 \cr & = {P_{{\text{atm}}}} + 1052\,N{m^{ - 2}} \cr} $$
$$\therefore $$ Pressure within the bubble in excess of atmospheric pressure $$ = 1052\,N{m^{ - 2}}.$$

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Basic Physics >> Mechanical Properties of Solids and Fluids

Releted Question 1

The following four wires are made of the same material. Which of these will have the largest extension when the same tension is applied?

A. $$length=50\,cm, \,\,diameter=0.5 \,mm$$
B. $$length = 100 \,cm, \,\,diameter= 1 \,mm$$
C. $$length= 200 \,cm, \,\,diameter= 2 \,mm$$
D. $$length=300 \,cm, \,\,diameter =3 \,mm$$
Releted Question 2

A U-tube of uniform cross section (see figure) is partially filled with a liquid I. Another liquid II which does not mix with liquid I is poured into one side. It is found that the liquid levels of the two sides of the tube are the same, while the level of liquid I has risen by $$2 \,cm.$$  If the specific gravity of liquid I is $$1.1,$$  the specific gravity of liquid II must be-
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A. $$1.12$$
B. $$1.1$$
C. $$1.05$$
D. $$1.0$$
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A homogeneous solid cylinder of length $$L\left( {L < \frac{H}{2}} \right),$$   cross-sectional area $$\frac{A}{5}$$ is immersed such that it floats with its axis vertical at the liquid-liquid interface with length $$\frac{L}{4}$$ in the denser liquid as shown in the figure. The lower density liquid is open to atmosphere having pressure $${P_0}.$$ Then density $$D$$ of solid is given by-
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A. $$\frac{5}{4}d$$
B. $$\frac{4}{5}d$$
C. $$4d$$
D. $$\frac{d}{5}$$
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A large open tank has two holes in the wall. One is a square hole of side $$L$$ at a depth $$y$$ from the top and the other is a circular hole of radius $$R$$ at a depth $$4y$$  from the top. When the tank is completely filled with water, the quantities of water flowing out per second from both holes are the same. Then, $$R$$ is equal to-

A. $$\frac{L}{{\sqrt {2\pi } }}$$
B. $$2\pi L$$
C. $$L$$
D. $$\frac{L}{{2\pi }}$$

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