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  • A rectangular film of liquid is extended from <img alt="\left( {4{\rm cm} \times 2{\rm cm}} \right)" src="https://learn.careers360.com/latex-image/?%5Cleft%28%20%7B4%7B%5Crm%20cm%7D%20%5Ctimes%202%

A rectangular film of liquid is extended from \left( {4{\rm cm} \times 2{\rm cm}} \right) to \left( {5{\rm cm} \times 4{\rm cm}} \right). If the work done is 3 \times 10^{ - 4} {\rm J}, the value of the surface tension of the liquid is

Option: 1

0.250 N m-1


Option: 2

0.125 N m-1


Option: 3

0.2 N m-1


Option: 4

8.0 N m-1


Answers (1)

best_answer

Initial area of the film       A_i = 4 \times 2 = 8 \ cm^2 = 8 \times10^{-4} \ m^2

Final area of the film       A_f = 5 \times 4 = 20 \ cm^2 = 20 \times10^{-4} \ m^2

Thus change in area    \Delta A = (20-8) \ cm^2 = 12 \times10^{-4} \ m^2

Work done     W=3 \times10^{-4} \ J

Using for soap films        W=S(2ΔA)                     where S is the surface tension

∴    3×10−4=S×2×12×10-4                 

?S=0.125  Nm-1

Posted by

Kuldeep Maurya

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