Question

The work done to form a layer of soap solution of size $ 10\times 10\,cm $ 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, $=2 \times 10 \,\times 10 \,cm ^{2}=2 \times 10^{-2} m ^{2}$
$T=3 \times 10^{-2} N / m$
Hence, work done $=3 \times 10^{-2} \times 2 \times 10^{-2}$
$=6 \times 10^{-4} J$