BATCH
Surface
BASIC
Tension
MATHS
Surface Tension :
1) Surface Tension is the property of Liquid
surface.
2) The Property of Liquid Surface due to which
it tries to attain minimum Surface Area is
called Surface Tension.
3) A Small drop of Liquid is spherical in shape ,
because for given Volume , sphere has
minimum Surface Area.
Q 1)The rain drops are in spherical shape due to
A .Viscosity
B. Surface tension
C. Thrust on drop
D. Both A and B
Surface Tension is numerically equal to the force
acting per unit length of a hypothetical line drawn
on a liquid surface normal to it in either direction.
Q2) A beaker of radius 15 cm is filled with liquid of surface
tension 0.075 N/m. Force across an imaginary diameter on
the surface of liquid is
(A) 0.075 N
(B) 1.5 × 10–2 N
(C) 0.225 N
(D) 2.25 × 10–2 N
Liquid Film
Sliding wire
Q3) A thin liquid film formed between a U-shaped wire and a
light slider supports a weight of 1.5 × 10–2N(see figure). The
length of the slider is 30cm and its weight negligible. The
surface tension of the liquid film is
a) 0.1N/m
b) 0.05N/m
c) 0.025N/m
d) 0.0125N/m
Floating of Needle on Water surface
Lifting of Needle above water surface
Q4)
Q5)
Some important points
1) Soap decreases the surface tension of water , which
helps soap water to reach in pores of clothes and take
out dirt.
Surface Tension of a liquid decreases with rise in
Temperature and becomes ZERO at critical temperature,
2)
that is why hot soup tastes better than cold one
3) Surface Tension is a scalar quality. (However direction
of the force on the line on which it is calculated
can be known)
4) It depends on nature of liquid and its intermolecular
forces.
5) It depends on impurities added to a liquid
Surface Energy
1) Molecules on a liquid surface have some extra energy in
comparison to molecules in the interior. A liquid, thus, tends to
have the least surface to have minimum energy and most
stability
Surface Energy is nearly half of Heat Of Vapourisation
Surface Energy and Surface Tension
Liquid Film
Q6)
Q7)
Number of surfaces in liquid film and bubble
Q8)
Q9)
Q10)
(Energy of new drop/ Energy of Old Drop)
Q11)
Excess Pressure in a Liquid Drop
Liquid Drop experiences
Compressive stress due to
Excess Pressure on concave side
For Soap Bubble
Q12)
Q13) 0.04 cm liquid column balances the excess pressure
inside a soap bubble of radius 6 mm. Evaluate density of the
liquid. Surface tension of soap solution =0.03N/m
a)
b)
c)
d)
4x103 kg/m3
5x103 kg/m3
8x103 kg/m3
12x103 kg/m3
Q14) A soap bubble , having radius of 1mm,is blown from a
detergent solution having a surface tension of 2.5 x 10-2 N/m.
The pressure inside the bubble equals at a point Zo below the
free surface of water in a container. Taking g=10 m/s2,density
of water=103 kg/m2,the value of Zo is
[NEET 2019]
a)
b)
c)
d)
0.5 cm
100 cm
10 cm
1 cm
Contact Angle
The angle between tangent to the liquid surface at the
point of contact and tangent to solid surface, measured
inside the liquid is termed as angle of contact.
➢ For pure water and perfectly clean glass,the
angle of contact is 0o
➢ For ordinary water and glass,it lies between
8o and 18o.
➢ For pure water and pure silver,the angle of
contact is 90o
➢ For mercury and perfectly clean glass,the angle
of contact is 135o
Q15)
Cohesive Force: Force of attraction between
molecules of same kind.
Adhesive Force: Force of attraction between
molecules of different kind.
Capillarity
If a capillary tube of glass is dipped in liquid like
water, the liquid rises in the tube, but when the
capillary tube is dipped in a liquid like mercury, the
level of liquid falls in the tube. This phenomenon of
rise or fall of a liquid in the capillary is called
capillarity
Height of Capillary Rise
Q16) If the surface tension of water is 0.06 N/m then the
capillary rise in a tube of diameter 1mm is (θ=0o)
a) 3.86 cm
b) 3.12 cm
c) 2.4 cm
d) 1.22 cm
Q17) Water rises to a height of 10 cm in a capillary tube and
mercury falls to a depth of 3.5 cm in the same capillary tube.
If the density of mercury is 13.6 gm/cc and its angle of
contact is 135o and density of water is 1 gm/cc and its angle
of contact is 0o, then the ratio of surface tensions of the two
liquids is (cos 135o=0.7)
[MP PMT 1988;EAMCET 2003]
a)
b)
c)
d)
1:14
5:34
1:5
5:27
Q18)
Q19)
a)
b)
c)
d)
2.0 cm
4.0 cm
4/ 𝟑 cm
2 𝟐 cm
Q20)
Q21)
a)
b)
c)
d)
2 cm
4 cm
8 cm
16 cm
Q22) A capillary tube of radius R is immersed in water and
water rises in it to a height H.Mass of water in the capillary
tube is M.If the radius of the tube is doubled,mass of water
that will rise in the capillary tube will now be
[RPMT 1997;RPET 1999;CPMT 2002]
a)
b)
c)
d)
M
2M
M/2
4M
Q23)
a)
b)
c)
d)
2.5 g
5.0 g
10 g
20 g
[NEET 2020]
Radius of Tube(r) and Radius of Meniscus(R)
Capillary Tube of Insufficient height
If tube is cut
Q24)
Q25)