Question

A rectangular film of liquid is extended from 2 cm × 3.5 cm to 2 cm × 4.5 cm. If the work done is 6.4 × 10⁻⁵ J, the surface tension of the liquid is ______.

Options

• 0.16 N/m

• 0.24 N/m

• 0.32 N/m

• 0.48 N/m

Answer 1

A rectangular film of liquid is extended from 2 cm × 3.5 cm to 2 cm × 4.5 cm. If the work done is 6.4 × 10⁻⁵ J, the surface tension of the liquid is 0.48 N/m.

Explanation:

Given: Work done (W) = 6.4 × 10⁻⁵ J

Initial area (A₁) = 2 × 3.5 = 7 cm²

Final area (A₂) = 2 × 4.5 = 9 cm²

ΔA = A₂ − A₁

= 9 − 2

= 2 cm²

Work done in increasing surface area:

W = 2TΔA    ...(factor 2 for two surfaces)

⇒ 6.4 × 10⁻⁵ = 2T × (2 × 10⁻⁴)

⇒ T = `(6.4 xx 10^-5)/(4 xx 10^-4)`

= 0.16 N/m