Question

AB is a glass tube of uniform cross–section. V is a value which isolates ends A and B when closed. A bubble of radius r and 2r is blown at the two ends of the tube. The end A is inside an enclosure having air at pressure P. The same for bubble at end B is 2P as shown in Fig. On openning value V air will flow from B to A if (S = surface of tension).

(1) p = 2S/r

(2) p > 2S/r

(3) P < 2S/r

(4) P = S/r

Answer 1

(2) p > 2S/r

P_A = Total pressure of air inside bubble A = P + 4S/r

P_B = The total pressure of air inside bubble B = 2P + 4S/2r = 2p + 2S/r

On opening value V air will flow from B to A if P_B > P_A