Question Details

Radius of a soap bubble is increased from R to 2R work done in this process in terms of surface tension is

Options

A

24π R²S

B

48π R²S

C

12π R²S

D

36π R²S

Correct Answer :

24π R²S

Solution :

The correct option is 24π R²S.

Underlying Concept:
A soap bubble has two free surfaces in contact with air (one inner surface and one outer surface). Therefore, when calculating the total surface area of a soap bubble, we must multiply the area of a single sphere by 2.
The work done (W) in expanding a soap bubble is equal to the product of its surface tension (S) and the increase in its total surface area (ΔA):
W=S×ΔA

Step-by-Step Derivation:

1. Initial Surface Area (A1):
For an initial radius R, the total initial surface area is:
A1=2×(4πR2)=8πR2

2. Final Surface Area (A2):
When the radius is increased to 2R, the total final surface area becomes:
A2=2×[4π(2R)2]=2×(16πR2)=32πR2

3. Change in Surface Area (ΔA):
The increase in surface area is:
ΔA=A2-A1

Substituting the values:
ΔA=32πR2-8πR2=24πR2

4. Work Done (W):
Using the relation for work done:
W=S×ΔA

Substituting the change in area:
W=S×24πR2=24πR2S

Therefore, the work done in this process is 24π R²S.

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