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NCERT Solutions for class 11 Physics | Chapter 10 - Mechanical Properties of Fluids

(1) Surface tension of a soap solution is 1.9 × 10-2 N/m. work done in blowing a bubble of 2.0 cm diameter will be
[A] 7.6 × 10-6 p J
[B] 15.2 × 10-6 p J
[C] 1.9 × 10-6 p J
[D] 1 × 10-4 p J
Answer: 15.2 × 10-6 p J
(2) A drop of liquid of diameter 2.8 mm beaks up into 125 identical drops. The change in energy is nearly ( S.T. of liquid = 75 × 10-3 N/m)
[A] Zero
[B] 19 × 10-7 J
[C] 46 × 10-7 J
[D] 74 × 10-7 J
Answer: 74 × 10-7 J

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(3) The pressure just below the meniscus of water
[A] Is greater than just above it
[B] Is less than just above it
[C] Is same as just above it
[D] Is always equal to atmospheric pressure.
Answer: Is less than just above it
(4) A liquid does not wet the surface of a solid if the angle of contact is
[A] Zero
[B] An acute one
[C] 45?
[D] An obtuse one
Answer: An obtuse one
(5) Rain drops are spherical in shape because of
[A] Surface tension
[B] Capillary
[C] Downward motion
[D] Acceleration due to gravity
Answer: Surface tension
(6) A tank contains water on top of mercury. A cube of iron .06 m along each edge is sitting upright in equilibrium in the liquid.

Density of iron =7.7X103 kg/m3

Density of mercury = 13.6X103 kg/m3

Which one of the following is true

[A] x=32mm and y=28mm
[B] The pressure difference (p2-p1) is 4632 N/m2
[C] The weight of the mercury cube is 16.632 g
[D] None of these
Answer: The weight of the mercury cube is 16.632 g
(7) Water rises in a capillary tube to a certain height such that the upward force due to surface tension is balanced by 75 × 10-4 N, forces due to the weight of the liquid. If the surface tension of water is 6 × 10-2 N/m, the inner-circumference of the capillary must be
[A] 1.25 × 10-2 m
[B] 0.50 × 10-2 m
[C] 6.5 × 10-2 m
[D] 12.5 × 10-2 m
Answer: 12.5 × 10-2 m
(8) A number of small drops of mercury coalesce adiabatically to form a single drop. The temperature of
[A] drop
[B] Increases
[C] Is infinite
[D] Remains unchanged
Answer: Remains unchanged
(9) At critical temperature, the surface tension of a liquid
[A] Is zero
[B] Is infinity
[C] Is the same as that at any other temperature
[D] Can not be determined
Answer: Is zero
(10) 5 g of water rises in the bore of capillary tube when it is dipped in water. If the radius of bore capillary tube is doubled, the mass of water that rises in the capillary tube above the outside water level is
[A] 1.5 g
[B] 10 g
[C] 5 g
[D] 15 g
Answer: 10 g
(11) If the surface of a liquid is plane, then the angle of contact of the liquid with the walls of container is
[A] Acute angle
[B] Obtuse angle
[C] 90°
[D] 0°
Answer: 0°
(12) Surface tension may be defined as
[A] The work done per unit area in increasing the surface area of a liquid under isothermal condition
[B] The work done per unit area in increasing the surface area of a liquid under adiabatic condition
[C] The work done per unit area in increasing the surface is of a liquid under both isothermal and adiabatic conditions.
[D] Free surface energy per init volume
Answer: The work done per unit area in increasing the surface area of a liquid under isothermal condition
(13) The height of water in a capillary tube of radius 2 cm is 4 cm. what should be the radius of capillary, if the water rises to 8 cm in tube?
[A] 1 cm
[B] 0.1 cm
[C] 2 cm
[D] 4 cm
Answer: 1 cm
(14) The rise of a liquid in a capillary tube does not depend upon
[A] Angle of contact
[B] Density of the liquid
[C] Radius of the capillary tube
[D] Atmospheric pressure
Answer: Atmospheric pressure
(15) A capillary tube is placed vertically in a liquid. If the cohesive force is less than the adhesive force, then
[A] The meniscus will be convex upwards
[B] The liquid will wet the solid
[C] The angle of contact will be obtuse
[D] The liquid will drip in the capillary tube
Answer: The liquid will wet the solid
(16) A capillary tube when immersed vertically in a liquid records a rise of 3 cm. if the tube is immersed in the liquid at an angle of 60° with the vertical, then length of the liquid column along the tube will be
[A] 2 cm
[B] 3 cm
[C] 6 cm
[D] 9 cm
Answer: 6 cm
(17) Amount of energy required to blow a bubble of radius 5 cm, is (Surface tension of soap is 30 × 10-2 N/m)
[A] 1.88 J
[B] 1.88 × 10-1 J
[C] 1.88 × 10-2 J
[D] 1.88 × 10 J
Answer: 1.88 × 10-2 J
(18) Meniscus of mercury in capillary is
[A] Concave
[B] Convex
[C] Plane
[D] Cylindrical
Answer: Convex
(19) Rain drops are spherical because of
[A] Gravitational force
[B] Surface tension
[C] Air resistance
[D] Low viscosity of water
Answer: Surface tension
(20) A capillary tube of radius r can support a liquid of weight 6.28 × 10-4 N. if the surface tension of the liquid is 5 × 10-2 N/m. the radius of capillary must be
[A] 2.5 × 10-3 m
[B] 2.0 × 10-4 m
[C] 1.5 × 10-3 m
[D] 2.0 × 10-3 m
Answer: 2.0 × 10-3 m

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