Question

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

• A. $0.250 \, N \, m^{- 1}$
• B. $0.125 \, N \, m^{- 1}$
• C. $0.2 \, N \, m^{- 1}$
• D. $8.0 \, N \, m^{- 1}$

Answer 1

Answer: (B)

$W=2\left(A_{f} - A_{i}\right)T$
$\Rightarrow T=\frac{W}{\left(A_{f} - A_{i}\right) \times 2}$
$=\frac{3 \times 10^{- 4} \, J}{2 \left[5 \times 4 \times 10^{- 4} - 4 \times 2 \times 10^{- 4}\right]}$
$=0.125 \, N \, m^{- 1}$