# Two soap bubbles A and B (rA < rB) isolated from one another are blown on the two ends of a U–tube as shown

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Two soap bubbles A and B (rA < rB) 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.

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

Let P be the atmospheric pressure.

PA = Total pressure of air inside bubble A

= P + 4S/rA

PB = Total pressure of air inside bubble B.

= p + 4S/rB

Since rA < rB ; PA > PB . 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.