Define Viscosity MCQ

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MCQ on Define Viscosity for NEET Students

The velocity of water in a river is

(A) the same everywhere.

(B) less in the middle and more near its banks.

(C) more in the middle and less near its banks.

(D) increases from one bank to another bank.

Option c – more in the middle and less near its banks.

A flow of liquid is streamlined if the Reynold number is

(A) less than 2000

(B) between 3000 and 4000

(C) between 2000 to 3000

(D) between 4000 to 5000

Option a – less than 2000

Water is flowing through a tube of the non-uniform cross-section. The ratio of the radius at the entry and exit end of the pipe is 4 : 3. Then the ratio of velocities at the entry and exit of the liquid is

(A) 16 : 9

(B) 9:16

(C) 4 : 3

(D) 3 : 4

Option b – 9:16

The direction of viscous force acting on a liquid layer is

(A) not defined as the force in a fluid is tensor quantity.

(B) opposite to that of the flow of layers.

(C) tangential to the layer.

(D) parallel to the layer.

Option c – tangential to the layer.

Assertion: Critical velocity is different from terminal velocity. Reason: The constant velocity of the fall of a body through a viscous fluid is called terminal velocity.

(A) The assertion is True, Reason is True; Reason is a correct explanation for Assertion.

(B) The assertion is True, and Reason is True; Reason is not a correct explanation for Assertion.

(C) The assertion is True, Reason is False.

(D) The assertion is False, Reason is True.

Option b – The assertion is True, and Reason is True; Reason is not a correct explanation for Assertion.

The working of an atomizer is based on

(A) Bernoulli’s theorem.

(B) Boyle’s law,

(C) Archimedes’ principle.

(D) Newton’s law of motion.

Option a – Bernoulli’s theorem.

Bernoulli’s equation is valid for

(A) constant, viscous, incompressible. temperature-dependent flow.

(B) variable, non-viscous, incompressible. temperature-independent flow.

(C) constant, non-viscous, incompressible. temperature-independent flow.

(D) variable, non-viscous, incompressible. temperature-dependent flow.

Option c – constant, non-viscous, incompressible. temperature-independent flow.

A fluid flows through a pipe of length l. Its radius at one end is r and its velocity is v. If the radius is increased to 3r, then its new velocity will be

(A) 3v

(B) v/9

(C) v/3

(D) 9v

Option b – v/9

A spaceship entering the earth’s atmosphere is likely to catch fire. This is due to

(A) the surface tension of air.

(B) the viscosity of air.

(C) the greater proportion of oxygen in the atmosphere at high altitudes

(D) the temperature of the upper atmosphere.

Option b – the viscosity of air.

The viscosity of an ideal fluid …….

(A) zero

(B) between 0.5 and 1

(C) equal to 1

(D) infinity

Option a – zero

Water is flowing through a horizontal pipe of the non-uniform cross-section. At the extremely narrow portion of the pipe, the water will have

(A) maximum speed and the least pressure.

(B) the maximum pressure and least speed.

(C) both pressure and speed least.

(D) both pressure and speed maximum.

Option a – maximum speed and the least pressure.

In the case of a streamlined flow of liquid through a pipe of uniform cross-sectional area, all the streamlines are

(A) divided into rectangular blocks.

(B) divided into plane layers.

(C) parallel to the axis of the tube.

(D) circular in shape.

Option c – parallel to the axis of the tube.

The velocity of falling raindrops attains limited value. This is due to ………

(A) upthrust due to air

(B) surface tension

(C) the viscous force exerted by air

(D) air current

Option c – the viscous force exerted by air

In a laminar flow, the velocity of flow at a point in the liquid

(A) does not vary with time.

(B) may vary in direction but not in magnitude.

(C) may vary both in magnitude and direction.

(D) may vary in magnitude but not in direction.

Option a – does not vary with time.

A drop of liquid having a radius of 2 mm has a terminal velocity of 30 cm/s. The terminal velocity of a drop of 1 mm radius will be

(A) 30 cm/s

(B) 22.5 cm/s

(C) 15 cm/s

(D) 7.5 cm/s

Option d – 7.5 cm/s

What remains unchanged along the axis in a venturi meter?

(A) pressure energy of flowing liquid

(B) K.E. of flowing liquid

(C) P.E. of flowing liquid

(D) Both K.E. and P.E.

Option c – P.E. of flowing liquid

Two small spheres of radii r and 3r fall through a viscous liquid with the same constant speed. The viscous forces experienced by them are in the ratio

(A) 1 : 9

(B) 1 : 3

(C) 9 : 1

(D) 3 : 1

Option b – 1 : 3

Which of the following statement is CORRECT?

(A) The viscosity of a liquid decreases with temperature while that of gas increases with temperature.

(B) The viscosity of liquid and gases increases with temperature.

(C) The viscosity of liquid and gases decreases with temperature.

(D) The viscosity of the liquid increases with temperature while that of gas decreases with temperature.

Option a – The viscosity of a liquid decreases with temperature while that of gas increases with temperature.

In the case of streamlined flow, the velocity of the liquid at the bottom layer is

(A) zero.

(B) infinity.

(C) mean of velocities of all layers.

(D) maximum.

Option a – zero.

The coefficient of viscosity can be defined as

(A) longitudinal stress to strain.

(B) shearing stress per unit length.

(C) shearing stress to strain rate.

(D) strain per unit area.

Option c – shearing stress to strain rate.

The venturi meter measures the pressure difference by measuring ……….. difference.

(A) height

(B) temperature

(C) velocity

(D) volume

Option a – height

Two vessels have different base areas. They are filled with water to the same height. If the amount of water in one is 4 times that in the other, then the ratio of pressures on their bottoms will be

(A) 16 : 1

(B) 8 : 1

(C) 4 : 1

(D) 1 : 1

Option d – 1 : 1

The coefficient of viscosity for hot air is ( Define Viscosity MCQ )

(A) smaller than the coefficient of viscosity for cold air.

(B) greater than the coefficient of viscosity for cold air.

(C) same as the coefficient of viscosity for cold air.

(D) increases or decreases depending on the external pressure.

Option b – greater than the coefficient of viscosity for cold air.

A pipe, 2 cm in diameter, has a constriction of diameter 1.2 cm. What is the velocity of flow at the constriction, if the velocity of flow in the broader region of the pipe is 5 cm/s?

(A) 14.4 cm/s

(B) 28.8 cm/s

(C) 25 cm/s

(D) 30 cm/s

Option b – 28.8 cm/s

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A small cylinder of 2 cm diameter is connected to a large cylinder of 20 cm diameter and incompressible fluid is filled in the cylinders. If a force of 100 N is applied to the piston of the small cylinder, then the force exerted on the piston of the large cylinder will be

(A) 2,000 N

(B) 10000 N

(C) 20000 N

(D) 1000 N

Option b – 10000 N

When a fluid is flowing through a tube, then the reason for the viscous force acting between its different layers will be

(A) the transfer of momentum from one layer to another.

(B) transfer of energy from one layer to another.

(C) the equal velocity of the molecules.

(D) changing density along with the tube.

Option a – the transfer of momentum from one layer to another.

The velocity of the liquid flowing through a tube at a certain distance from the axis of the tube

(A) increases with distance.

(B) depends upon the length of the tube.

(C) decreases with distance.

(D) remains constant.

Option c – decreases with distance.

What is the barometric height of a liquid of density 3.4 g cm at a place where the mercury barometer is 76 cm?

(A) 270 cm

(B) 340 cm

(C) 304 cm

(D) 76 cm

Option c – 304 cm

In the case of turbulent flow, the velocity of the liquid molecules in contact with the walls of the tube

(A) is zero.

(B) is maximum.

(C) is equal to critical velocity.

(D) may have any value.

Option d – may have any value.

A small metal ball of mass ‘m’ is dropped in a liquid contained in a vessel, and attains a terminal velocity ‘v’. If a metal ball of the same material but of mass ‘8m’ is dropped in the same liquid then the terminal velocity will be

(A) V

(B) 2v

(C) 3v

(D) 6v

Option a – V

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