1.
A rectangular film of liquid is extended from (4cm×2cm)(4\,\text{cm} \times 2\,\text{cm}) to (5cm×4cm)(5\,\text{cm} \times 4\,\text{cm}). If the work done is 3×104J3 \times 10^{-4}\,\text{J}, the value of the surface tension of the liquid is