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The following is a method to determine the surface tension of liquids

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Important Questions on Viscosity and Surface Tension

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

Two light balls are suspended as shown in figure. When a stream of air passes through the space between them, the distance between the balls will

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

Three liquids of densities,

ρ_{1}, ρ_{2}

and

ρ_{3}

(with,

ρ_{1} > ρ_{2} > ρ_{3})

, having the same value of surface tension,

T

, rise to the same height in three identical capillaries. The angles of contact,

θ_{1}, θ_{2}

and

θ_{3}

obey

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

The ratio of surface tensions of mercury and water is given to be

7.5

, while the ratio of their densities is

13.6

. Their contact angles, with glass, are close to

135 °

and

0 °

, respectively. If it is observed that mercury gets depressed by an amount

h

in a capillary tube of radius

r_{1}

, while water rises by the same amount

h

in a capillary tube of radius

r_{2}

, then the ratio

\frac{r_{1}}{r_{2}}

is close to

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

Water rises upto a height

h

in a capillary tube on the surface of the earth. The value of

h

increases, if the capillary tube apparatus is kept

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

' M'

is the mass of water that rises in a capillary tube of radius

' r'

, then mass of water which will rise in a capillary tube of radius

' 2 r'

is:

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

A capillary tube of radius

r

is immersed in water and water rises in it to a height

h

. The mass of the water in the capillary is

5 g

. Another capillary tube of radius

2 r

is immersed in water. The mass of water that will rise in this tube is:

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

A capillary tube is immersed vertically in water and the height of the water column is

x

. When this arrangement is taken into a mine of depth d, the height of the water column is

y

. If R is the radius of earth, the ratio

\frac{x}{y}

is :

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

Two capillary tubes

P

and

Q

are dipped vertically in water. The height of water level in capillary tube

P

{(\frac{2}{3})}^{r d}

of the height in capillary tube

Q .

The ratio of their diameter is

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

In a capillary tube having area of cross-section

A

, the water rises to a height

h

. If the cross-sectional area is reduced to

\frac{A}{9}

, the rise of water in the capillary tube is

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

Two mercury drops (each of radius

r

) merge to form a bigger drop. The surface energy of the bigger drop, if

T

is the surface tension, is

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

Water rises to a height of

15 mm

in a capillary tube having cross-sectional area

A

. If cross-sectional area of the tube is made

\frac{A}{3}

then the water will rise to a height of

MEDIUM

Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

A big water drop is formed by the combination of

n

small water drops of equal radii. The ratio of the surface energy of

n

drops to the surface energy of the big drop is

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

In a capillary tube experiment, a vertical,

30 cm

long capillary tube is dipped in water. The water rises upto a height of

10 cm

due to capillary action. If this experiment is conducted in a freely falling elevator, the length of the water column becomes

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

A capillary tube made of glass of radius

0.15 mm

is dipped vertically in a beaker filled with methylene iodide (surface tension

= 0.05 N m^{- 1}

, density

= 667 kg m^{- 3}

) which rises to height

h

in the tube. It is observed that the two tangents drawn from liquid-glass interfaces (from opp. sides of the capillary) make an angle of

60 º

with one another. Then

h

is close to (

g = 10 m s^{- 2}

)

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

The rise of liquid in capillary is more than that of water in the same capillary. Which one of the following is the CORRECT reason?

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

Liquid

A

rises to a height of

10 cm

in a capillary tube and liquid

B

falls to a depth of

2 cm

in the same tube. The density of

A

and

B

are

1 g / {cm}^{3}

and

10 g / {cm}^{3}

respectively. The contact angle of

A

and

B

with the tube is

0 °

and

135 °

respectively. If the surface tension of

A

and

B

are

S_{A}

and

S_{B}

then the ratio

\frac{S_{B}}{S_{A}}

MEDIUM

Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

The lower end of a capillary tube is dipped into water and it is observed that the water in capillary tube rises by

7.5 cm

. Find the radius of the capillary tube used, if surface tension of water is

7.5 \times 10^{- 2} N m^{- 1}

? Angle of contact between water and glass is

0 °

and acceleration due to gravity is

10 m s^{- 2}

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

Water rises to a height 'h' in capillary tube. If the length of capillary tube above the surface of water is made less than 'h', then:

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

A soap bubble of radius

r

is blown up to form a bubble of radius

2 r

under isothermal conditions. If

σ

is the surface tension of the soap solution, the energy spent in the process is

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Physics>Mechanics>Viscosity and Surface Tension>Capillarity and Capillary Action

A rectangular film of liquid is extended from

(4 cm \times 2 cm)

(5 cm \times 4 cm)

. If the work done is

3 \times 10^{- 4} J

, the value of the surface tension of the liquid is

The following is a method to determine the surface tension of liquids

Important Questions on Viscosity and Surface Tension

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