Two soap bubbles having unequal radii are joined together through a small tube. What happens to the air?

Air moves from the larger bubble to the smaller one until they are equal in size
Air moves from the larger bubble to the smaller one until their sizes swap
Air moves from the smaller bubble into the larger one
No air movement occurs

Correct answer: Air moves from the smaller bubble into the larger one

Solution

The excess pressure inside a soap bubble varies inversely with radius (P = 4T/r). The smaller bubble has higher pressure, so air flows from it into the larger (lower-pressure) bubble, making the small one shrink and the large one grow.

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