devarshi-dt-logo

Question:

Two soap bubbles A and B are kept in a closed chamber where the air is maintained at pressure 8 N/m². The radii of bubble A and B are 2 cm and 4 cm, respectively. Surface tension of the soap water used to make bubbles is 0.04 N/m. Find the ratio nB/nA, where nA and nB are the number of moles of air in bubbles A and B, respectively. (Neglect the effect of gravity).

Solution:

PA=P0+4T/RA=8 + 4*(0.04)/0.02 = 16 N/m²
PB=P0+4T/RB=8 + 4*(0.04)/0.04 = 12 N/m²
nB/nA = (PB/PA)(RB/RA)³ = (12/16)(0.04/0.02)³ = (3/4)*(2)³ = 6.