Work done in increasing the size of a soap bubble from a radius of 3 cm to 5 cm is nearly (Surface tension of soap solution = 0.03 Nm⁻¹)?

W = (surface energy)final - (surface energy)initial
W = T × 4π [(5 × 10⁻²)² - (3 × 10⁻²)²] × 2
= 4π × 0.03 × 16 × 10⁻⁴ × 2
= 4π × 0.48 × 10⁻⁴ × 2
= 1.92π × 10⁻⁴ × 2
= 3.94π × 10⁻⁴ = 0.394π mJ ≈ 0.4π mJ