Question

The work done to form a layer of soap solution of size $10\times 10cm$ will be: (surface tension of soap solution is $3\times {10}^{-2}N/m$ )

• A. $\text{6 }\times \text{ 1}{\text{0}}^{\text{-2}}\text{J}$
• B. $\text{6 }\times \text{ 1}{\text{0}}^{\text{-4}}\text{J}$
• C. $\text{3 }\times \text{ 1}{\text{0}}^{\text{-2}}\text{J}$
• D. $\text{3 }\times \text{ 1}{\text{0}}^{\text{-4}}\text{J}$

Answer 1

Answer: (B)

Surface tension $T$ can be defined as the work done informing the soap film of unit surface area. Surface tension of a soap film is written as
$T=\frac{\text{ work done }}{\text{ area }}$
or work done $=T\times$ area
Here, $=2\times 10\times 10c{m}^2=2\times 10^{-2}{m}^2$
$T=3\times 10^{-2}N/m$
Hence, work done $=3\times 10^{-2}\times 2\times 10^{-2}$
$=6\times 10^{-4}J$