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With the increase in temperature viscosity of a liquid -

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Important Questions on Viscosity and Surface Tension

EASY

Physics>Mechanics>Viscosity and Surface Tension>Viscosity

The velocity of upper layer of water in a river is

36 km h^{- 1}

. Shearing stress between horizontal layers of water is

10^{- 3} N m^{- 2}

. Depth of the river is _____

m

. (Co-efficient of viscosity of water is

10^{- 2} Pa s

)

EASY

Physics>Mechanics>Viscosity and Surface Tension>Viscosity

A flat plate of area $10 {cm}^{2}$ is separated form a large plate by a layer of Glycerine $1 mm$ thick. If the coefficient of viscosity of Glycerine is $20$ poise, the force required to keep the plate moving with a velocity of $1 cm s^{- 1}$ is

EASY

Physics>Mechanics>Viscosity and Surface Tension>Viscosity

p

is the density and

η

is coefficient of viscosity of fluid which flows with a speed

v

in the pipe of diameter

d

, the correct formula for Reynolds number

R_{e}

HARD

Physics>Mechanics>Viscosity and Surface Tension>Viscosity

Two tubes of radii

r_{1}

and

r_{2}

and lengths

l_{1}

and

l_{2,}

respectively, are connected in series and a liquid flows through each of them in stream line conditions.

P_{1}

and

P_{2}

are pressure differences across the two tubes. If

P_{2}

4 P_{1}

and

l_{2}

\frac{l_{1}}{4}

then the radius

r_{2}

will be equal to :

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

A solid sphere of volume

V

experiences a viscous force

F

when descending with a speed

v

in a liquid. If another solid sphere of volume

27 V

descends with the same speed

v

in the same liquid, it experiences a viscous force

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

Statement (A): When the temperature increases the viscosity of gases increases and the viscosity of liquids decreases.

Statement (B): Water does not wet an oily glass because cohesive force of oil is less than that of water.

Statement (C) : A liquid will wet a surface of a solid if the angle of contact is greater than $90 °$ .

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

Oil is used for frying food materials rather than water, since oil

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

In an experiment to verify Stokes law, a small spherical ball of radius

r

and density

ρ

falls under gravity through a distance

h

in air before entering a tank of water. If the terminal velocity of the ball inside water is same as its velocity just before entering the water surface, then the value of

h

is proportional to: (ignore viscosity of air)

HARD

Physics>Mechanics>Viscosity and Surface Tension>Viscosity

A steel ball is dropped in a viscous liquid. The distance of the steel ball from the top of the liquid is shown below. The terminal velocity of the ball is closest to

Question Image

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

The velocity of a small ball of mass

M

and density

ρ

, when dropped in a container filled with glycerine becomes constant after some time. If the density of glycerine is

\frac{ρ}{2}

, then the viscous force acting on the ball will be:

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Which of the following option correctly describes the variation of the speed

υ

and acceleration 'a' of a point mass falling vertically in a viscous medium that applies a force

F = - k υ

, where 'k' is a constant, on the body? (Graphs are schematic and not drown to scale)

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

The velocity of water in a river is

18 km h^{- 1}

near the surface. If the river is

5 m

deep, find the shearing stress between the horizontal layers of water. The coefficient of viscosity of water

= 10^{- 2} poise

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

Eight drops of water, each of radius

2 m m

are falling through air at a terminal velocity of

8 c m s^{- 1}

. If they coalesce to from a single drop, then the terminal velocity of combined drop will be:

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

The velocity of water in a river is

18 km h^{- 1}

near the surface. If the river is

5 m

deep, find the shearing stress between the horizontal layers of water. The coefficient of

viscosity of water = 10^{- 2} poise

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

A solid sphere, of radius R acquires a terminal velocity

v_{1}

when falling (due to gravity) through a viscous fluid having a coefficient of viscosity

η .

The sphere is broken into 27 identical solid spheres. If each of these spheres acquires a terminal velocity,

v_{2},

when falling through the same fluid, the ratio

(\frac{v_{1}}{v_{2}})

equals:

EASY

Physics>Mechanics>Viscosity and Surface Tension>Viscosity

Two rain drops falling through air have radii in the ratio

1 : 2

. They will have terminal velocity in the ratio

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

A rain drop of radius

0.3 mm

has a terminal velocity in air of

1 m s^{- 1}

. The viscosity of air is

8 \times 10^{- 5}

poise. The viscous force on it is

EASY

Physics>Mechanics>Viscosity and Surface Tension>Viscosity

Identify the incorrect statement regarding Reynold's number

(R_{e}) :

HARD

Physics>Mechanics>Viscosity and Surface Tension>Viscosity

Water from a pipe is coming at a rate of

100

liters per minute. If the radius of the pipe is

5 c m,

the Reynolds number for the flow is of the order of: (density of water =

100 k g / m^{3},

coefficient of viscosity of water

= 1 m P a s)

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Physics>Mechanics>Viscosity and Surface Tension>Viscosity

If it takes 5 minutes to fill a 15 litre bucket from a water tap of diameter

\frac{2}{\sqrt{π}} c m

then the Reynolds number for the flow is (density of water =

10^{3} k g / m^{3} a n d v i s c o s i t y o f w a t e r = 10^{- 3} P a . s

) close to:

With the increase in temperature viscosity of a liquid -

Important Questions on Viscosity and Surface Tension

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