Air is pushed into a soap bubble of radius r to double its radius. If

1.	Air is pushed into a soap bubble of radius r to double its radius. If the surface tension of the soap solution is S, the work done in the process is (a) 8πr2S (b) 12πr2S (c) 16πr2S (d) 24πr2S.
Answer» The correct answer is (d) 24πr²S. Explanation: The surface tension S is equal to surface energy per unit area, S = U/A →U = SA The total area of the soap bubble =24πr² =8πr² The total surface energy of the original bubble =8πr²S The total surface area of the expanded bubble = 24π(2r)² =32πr² The total surface energy of the expanded bubble =32πr²S The work done in the process = increase in the surface energy of the bubble =32πr²S - 8πr²S =24πr²S

Air is pushed into a soap bubble of radius r to double its radius. If the surface tension of the soap solution is S, the work done in the process is (a) 8πr2S (b) 12πr2S (c) 16πr2S (d) 24πr2S.

Answer»

The correct answer is (d) 24πr²S.

Explanation:

The surface tension S is equal to surface energy per unit area, S = U/A

→U = SA

The total area of the soap bubble =2*4πr² =8πr²

The total surface energy of the original bubble =8πr²S

The total surface area of the expanded bubble = 2*4π(2r)² =32πr²

The total surface energy of the expanded bubble =32πr²S

The work done in the process = increase in the surface energy of the bubble =32πr²S - 8πr²S =24πr²S