A rectangular film of liquid is extended from (4 cm×2 cm) to (5 cm×4 cm). If the work done is 3×10^(-4) J, the value of the surface tension of the liquid is

Correct answer: (B) 0.125 N m^(-1). W=2A_f-A_iT ⇒T=W/(A_f-A_i×2) =(3×10^(-4) J)/(25×4×10^(-4)-4×2×10^(-4)) =0.125 N m^(-1)

Q101 / 180 · NEET 2016 (Phase 2) · Physics

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

W = 2 (A_{f} - A_{i}) T

\Rightarrow T = \frac{W}{(A_{f} - A_{i}) \times 2}

= \frac{3 \times 10^{- 4} J}{2 [5 \times 4 \times 10^{- 4} - 4 \times 2 \times 10^{- 4}]}

= 0.125 N m^{- 1}

Hence, the correct answer is option: 'B'.