Question

Calculate the difference of pressure between inside and outside of a (i) spherical soap bubble in air, (ii) air bubble in water, and (iii) spherical drop of water, each of radius 1 mm. Given surface tension of water = 7.2 × 10^–2 Nm^–1 and surface tension of soap solution = 2.5 × 10^–2 Nm^–1. 

Answer 1

(i) Excess pressure inside a soap bubble of radius r is

(ii) Excess pressure inside an air bubble in water

(iii) Excess pressure inside a spherical drop of water =2T ′/ r

= 144 Nm^–2.