Question

Two soap bubbles A and B (r_A < r_B) isolated from one another are blown on the two ends of a U–tube as shown in Fig. V is a valve that isolates two bubbles from one another. On opening value V

(1) There is no flow of air from A to B or vice-versa 

(2) Air flows from B to A till the size of the two become same. 

(3) Air flows from A to B till either B brusts or A becomes extinct. 

(4) Air alternatively flows from A to B and vice-versa.

Answer 1

(3) Air flows from A to B till either B brusts or A becomes extinct. 

Let P be the atmospheric pressure.

P_A = Total pressure of air inside bubble A

= P + 4S/r_A

P_B = Total pressure of air inside bubble B.

= p + 4S/r_B

Since r_A < r_B ; P_A > P_B . On opening value V; air flows from region of higher pressure to lower pressure i.e. air flows from A to B, till either B brusts or A becomes extint.