Surface Tension Test

Result

Surface Tension Test - 7

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Weekly Quiz Competition

Question 1
1 / -0

When two soap bubbles of radius r₁ and r₂ (r₂>r₁) coalesce, the radius of curvature of the common surface is

A
r₂ − r₁

B

C

D
r₂ + r₁

Solution

If P₁ and P₂ are the excess pressure on the two sides of the interface, P = P₂−P₁
Question 2
1 / -0

The excess of pressure inside a soap bubble than that of the outer pressure is

A
2T/r

B
4T/r

C
T/2r

D
T/r

Solution

The excess of pressure inside a soap bubble = 4T/r
Question 3
1 / -0

The pressure of air in a soap bubble of 0.7cm diameter is 8 mm of water above the pressure outside. The surface tension of the soap solution is

A
100 dyne/cm

B
68.66 dyne/cm

C
137 dyne/cm

D
150 dyne/cm

Solution
Question 4
1 / -0

The pressure inside two soap bubbles are 1.01 and 1.02 atmospheres. The ratio between their volumes is

A
102 : 101

B
(102)³ : (101)³

C
8 : 1

D
2 : 1

Solution

Outside pressure = 1 atm

Pressure inside first bubble = 1.01 atm

Pressure inside second bubble = 1.02 atm

Excess pressure ΔP₁=1.01-1 = 0.01 atm

Excess pressure atm ΔP₂= 1.02-1 = 0.02 atm
Question 5
1 / -0

The radii of two soap bubbles are r₁ and r₂ . In isothermal conditions, two meet together in a vacuum. Then the radius of the resultant bubble is given by

A
R = (r₁+r₂)/2

B
R = r₁(r₁r₂+r₂)

C

D
R = r₁+ r₂

Solution

In isothermal condition -
Question 6
1 / -0

The excess pressure of one soap bubble is four times more than the other. Then the ratio of the volume of the first bubble to another one is

A
1 : 64

B
1 : 4

C
64 : 1

D
1 : 2

Solution
Question 7
1 / -0

There are two liquid drops of different radii. The excess pressure inside over the outside is:-

A
more in the big drop

B
more in the small drop

C
equal in both drops

D
there is no excess pressure inside the drops

Solution

The excess pressure inside a drop is always more than that on the outside.

and this excess pressure is given by, δP = 2T/R

Therefore, δP ∝ R⁻¹

Hence, the drop with a smaller radius will have a higher excess pressure inside the drop.
Question 8
1 / -0

Two soap bubbles have different radii but their surface tension is the same. Mark the correct statement

A
Internal pressure of the smaller bubble is higher than the internal pressure of the larger bubble

B
Pressure of the larger bubble is higher than the smaller bubble

C
Both bubbles have the same internal pressure

D
None of the above

Solution

Hence, the internal pressure of smaller bubble is larger than that of larger bubble.
Question 9
1 / -0

There is a horizontal film of soap solution. On it, a thread is placed in the form of a loop. The film is pierced inside the loop and the thread becomes a circular loop of radius R. If the surface tension of the loop be T, then what will be the tension in the thread?

A
πR²/T

B
πR²T

C
2πRT

D
2RT

Solution

Suppose tension in thread is F, then for small part ∆l of thread
Question 10
1 / -0

A large number of water drops each of radius r combines to have a drop of radius R. If the surface tension is T and the mechanical equivalent of heat is J, then the rise in temperature will be

A
2T/rJ

B
3T/RJ

C

D

Solution

Volume of n small drops = Volume of large drop .

Reduction in surface energy = T⋅ΔA