Question bank Class 12 Physics Chapter 2. Mechanical Properties of fluids
Standard:- 12th
Question Bank
Subject:- Physics
Chapter 2. Mechanical Properties
MCQ’s ( 1 Mark Each)
1) Insect moves over surface of water because of
a) Elasticity
b) Surface tension
c) Friction
d) Viscosity
Ans: b) Surface tension
2) The water droplets are spherical in free fall due to
a) gravity
b) intermolecular attraction
c) Surface tension
d) Viscosity
Ans: c) Surface tension
3) Surface tension of a liquid at critical temperature is
a) Infinity
b) Zero
c) Same as any other temperature
d) Can not be determined
Ans: b) Zero
4) Unit of coefficient of viscosity is
a) Ns/m
b) Ns2/m
c) Ns2/m2
d) Ns/m2
Ans: d) Ns/m2
a) 2:15) Two capillary tubes of radii 0.6 cm and 0.3 cm are dipped in the same liquid. The
ratio of heights through which the liquid will rise in the tubes is
b) 1:2
c) 4:1
d) 1:4
Ans: b) 1:2
6) The energy stored in a soap bubble of diameter 6 cm and T = 0.04 N/m is nearly
a) 0.9 × 10-3 J
b) 0.4 × 10-3 J
c) 0.7 × 10-3 J
d) 0.5 × 10-3 J
Ans: a) 0.9 × 10-3 J
7) Two stones with radii 1:2 fall from a great height through atmosphere. Their terminal
velocities are in the ratio
a) 2:1
b) 1:4
c) 4:1
d) 1:2
Ans: b) 1:4
Very Short Answer (VSA) ( 1 MARK Each )
1) What is surface film?
2) What are cohesive forces?
3) What will be the shape of liquid meniscus for obtuse angle of contact?
4) What is the net weight of a body when it falls with terminal velocity through a viscous
medium?
5) A square metal plate of area 100 cm2 moves parallel to another plate with a velocity
of 10 cm/s, both plates immersed in water. If the viscous force is 200 dyne and
viscosity of water is 0.01 poise, what is the distance between them? (Ans: 0.05 cm )
6) The relative velocity between two parallel layers of water is 8 cm/s and perpendicular
distance between them is 0.1 cm. Calculate the velocity gradient. (Ans:80 per second )
7) Water rises to a height of 20 mm in a capillary tube. If the radius made 1/3 rd of its
previous value, to what height will the water now rise in the tube? (Ans: 60 mm )
Short Answer I (SA1) ( 2 MARKS Each )
1) State properties of an ideal fluid.
2) Compare streamline flow and Turbulent flow.
3) Define surface tension and angle of contact.
4) Calculate the rise of water inside a clean glass capillary tube of radius 0.1 mm, when
immersed in water of surface tension 7 x 10-2 N/m. The angle of contact between
water and glass is zero, density of water is 1000 kg/m3 , g = 9.8 m/s2
( Ans: h = 0.1428 m)
5) A rain drop of radius 0.3 mm falls through air with a terminal velocity of 1 m/s. The
viscosity of air is 18 x 10-6 N-s /m2. Find the viscous force on the rain drop.
(Ans: F= 1.017 * 10 -7 N)
6) Two soap bubbles have radius in the ratio 2:3. Compare the works done in blowing
these bubbles. (Ans: 4:9)
Short Answer II (SA2) ( 3 MARKS Each )
1) Explain the phenomena of surface tension on the basis of molecular theory.
2) Obtain an expression for the capillary rise or fall using forces method.
3) State Stoke’s law and give two factors affecting angle of contact.
4) Twenty seven droplets of water, each of radius 0.1 mm coalesce into a single drop.
Find the change in surface energy. Surface tension of water is 0.072 N/m.
( Ans: W= 1.628 X 10 -7 J )
5) A u-tube is made up of capillaries of bore 1 mm and 2 mm respectively. The tube is
held vertically and partially filled with a liquid of surface tension 49 dyne/cm and
zero angle of contact. Calculate the density of liquid, if the difference in the levels of
the meniscus is 1.25 cm. take g = 980 cm/s2
( Ans: density of liquid = 0.8 g/ cm3 )
6) A rectangular wire frame of size 2 cm x 2 cm, is dipped in a soap solution and taken
out. A soap film is formed, it the size of the film is changed to 3 cm x 3 cm, Calculate
the work done in the process. The surface tension of soap film is 3 x 10-2 N/m.
( Ans: W= 3x 10-5 J )
Long Answer ( LA) ( 4 marks Each)
1) Derive the relation between surface energy & surface tension.
2) Obtain Laplace’s law of spherical membrane
3) Derive an expression for terminal velocity of the sphere falling under gravity through
a viscous medium.
