A rectangular film of liquid is extended from (4 cm × 2cm) to (5 cm × 4 cm). If the work done is 3 × 10–4 J, the value of the surface tension of the liquid is
Explanation:
Increase in surface area = (20 cm2-8 cm2)×2
= 12×2 cm2
= 24 cm2 (film has two surfaces)
So work done = T Δ S = T × 24 × 10-4 = 3×10-4
so T = 3/24 N/m = 1/8 Nm-1 = 0.125 N/m