Find the capillary pressure
(a) in mercury droplets of diameter `d = 1.5 mu m` ,
(b) inside a soap bubble diameter `d = 3.0 mm` if the surface tension of the soap water solution is `alpha = 45 mN//m`.

Explanation

(a) `Delta p = alpha ((1)/(d//2) + (1)/(d//2)) = (4 alpha)/(d)`
=`(4 xx 490 xx 10^-3)/(1.5 xx 10^-6) (N)/(m^2) = 1.307 xx 10^6 (N)/(m^2) = 12` atmosphere
(b) The soap bubble has two surfaces
so `Delta p = 2 alpha ((1)/(d//2) + (1)/(d//2)) = (8 alpha)/(d)`
=`(8 xx 45)/(3 xx 10^-3) xx 10^-3 = 1.2 xx 10^-3` atmosphere.