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Mechanical Properties of Fluids — Physics STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 SciencePhysicsMechanical Properties of Fluids4 Marks
Question
A rectangular wire frame of size $2 cm \times 2 cm$, is dipped in a soap solution and taken out. A soap film is formed, if the size of the film is changed to $3 cm \times 3 cm$, calculate the work done in the process. The surface tension of soap film is $3 \times 10^{-2} N / m$.
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Answer

Data: $A_1=2 \times 2 cm ^2=4 \times 10^{-4} m ^2$,
$A_2=3 \times 3 cm ^2=9 \times 10^{-4} m ^2, T =3 \times 10^{-2} N / m$
As the film has two surfaces, the work done is $W =2 T \left( A _2- A _1\right)$
$ =2\left(3 \times 10^{-2}\right)\left(9 \times 10^{-4} \times 10^{-4}\right)$
$=3.0 \times 10^{-5} J =30 \mu J $

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