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Question Bank [ 2022 ] — Physics STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 SciencePhysicsQuestion Bank [ 2022 ]3 Marks
Question
A rectangular wireframe 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 the soap film is $3 \times 10^{-2} N / m$.
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Answer

Given:
$A_1=2 \times 2 cm^2=4 \times 10^{-4} m^2 \\
A_2=3 \times 3 cm^2=9 \times 10^{-4} m^2 \\
T=3 \times 10^{-2} N / m$
To find:
The work done in the process
Solution:
As the film has two surfaces, the work done is
$W=2 T\left(A_2-A_1\right) \\
=2\left(3 \times 10^{-2}\right)\left(9 \times 10^{-4}-4 \times 10^{-4}\right) \\
=3 \times 10^{-5} J$

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