Surface Tension Test

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Surface Tension Test - 5

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Weekly Quiz Competition

Question 1
1 / -0

A spherical drop of oil of radius 1 cm is broken into 1000 droplets of equal radii. If the surface tension of oil is 50 dynes/cm, the work done is

A
18 π ergs

B
180 π ergs

C
1800 π ergs

D
8000 π ergs

Solution
Question 2
1 / -0

If the surface tension of a liquid is T, the gain in surface energy for an increase in liquid surface by A is

A
AT⁻¹

B
AT

C
A²T

D
A²T²

Solution

As we know,

Surface energy = surface tension × increment in area

= T×A
Question 3
1 / -0

The surface tension of a liquid at its boiling point

A
Becomes zero

B
Becomes infinity

C
is equal to the value at room temperature

D
is half to the value at the room temperature

Solution

As the temperature increases, surface tension decreases. At the boiling point, every molecule of a liquid is in motion from bottom to surface, and due to a rise in temperature, molecules lose the adhesion, and hence, surface tension becomes zero.
Question 4
1 / -0

The surface tension of liquid is 0.5 N/m. If a film is held on a ring of area 0.02 m², its surface energy is

A
5×10⁻² joule

B
2×10⁻² joule

C
4×10⁻⁴ joule

D
0.8×10⁻¹ joule

Solution

Surface energy = T × ΔA = 0.5 × 2 × (0.02) = 2 × 10 ⁻²J
Question 5
1 / -0

A liquid drop of diameter D breaks upto into 27 small drops of equal size. If the surface tension of the liquid is σ, then change in surface energy is

A
πD²σ

B
2πD²σ

C
3πD²σ

D
4πD²σ

Solution

Work done =
Question 6
1 / -0

One thousand small water drops of equal radii combine to form a big drop. The ratio of final surface energy to the total initial surface energy is

A
1000 : 1

B
1 : 1000

C
10 : 1

D
1 : 10

Solution

As volume remain constant therefore

R = n^1/3r
Question 7
1 / -0

A big drop of radius R is formed by 1000 small droplets of water, then the radius of small drop is

A
R/2

B
R/5

C
R/6

D
R/10

Solution
Question 8
1 / -0

8000 identical water drops are combined to form a big drop. Then the ratio of the final surface energy to the initial surface energy of all the drops together is

A
1 : 10

B
1 : 15

C
1 : 20

D
1 : 25

Solution

As volume remains constant R³ = 8000 r³ ∴ R = 20r
Question 9
1 / -0

When two small bubbles join to form a bigger one, energy is

A
Released

B
Absorbed

C
Both (1) and (2)

D
None of these

Solution

When water droplets merge to form a bigger drop the total surface area decreases. Since the molecules in the surface have greater potential energy, the potential energy of surface molecules in the bigger drop decreases from before the merger. In other terms, the surface energy per unit area is equal to the surface tension. Since the surface tension remains the same, the surface energy will be less in the merged bigger drop. Hence the energy is liberated in the process.
Question 10
1 / -0

A film of water is formed between two straight parallel wires of length 10cm each separated by 0.5 cm. If their separation is increased by 1 mm while still maintaining their parallelism, how much work will have to be done (Surface tension of water = 7.2 × 10⁻²N/m)

A
7.22×10⁻⁶ Joule

B
1.44×10⁻⁵ Joule

C
2.88×10⁻⁵ Joule

D
5.76×10⁻⁵ Joule

Solution

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Re-Attempt Weekly Quiz Competition

Surface Tension Test - 5

Result

Surface Tension Test - 5

Score

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Rank

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SHARING IS CARING

Question 1

18 π ergs

180 π ergs

1800 π ergs

8000 π ergs

Solution

Question 2

AT−1

AT

A2T

A2T2

Solution

Question 3

Becomes zero

Becomes infinity

is equal to the value at room temperature

is half to the value at the room temperature

Solution

Question 4

5×10−2 joule

2×10−2 joule

4×10−4 joule

0.8×10−1 joule

Solution

Question 5

πD2σ

2πD2σ

3πD2σ

4πD2σ

Solution

Question 6

1000 : 1

1 : 1000

10 : 1

1 : 10

Solution

Question 7

R/2

R/5

R/6

R/10

Solution

Question 8

1 : 10

1 : 15

1 : 20

1 : 25

Solution

Question 9

Released

Absorbed

Both (1) and (2)

None of these

Solution

Question 10

7.22×10−6 Joule

1.44×10−5 Joule

2.88×10−5 Joule

5.76×10−5 Joule

Solution

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AT⁻¹

A²T

A²T²

5×10⁻² joule

2×10⁻² joule

4×10⁻⁴ joule

0.8×10⁻¹ joule

πD²σ

2πD²σ

3πD²σ

4πD²σ

7.22×10⁻⁶ Joule

1.44×10⁻⁵ Joule

2.88×10⁻⁵ Joule

5.76×10⁻⁵ Joule