A large soap bubble in vacuum is produced by combining N identical soap bubbles, each of radius 2 mm. The final bubble radius is 10 mm. The process is isothermal and no gas is lost. Find N.
Physics · Properties of solid and fluid · properties of fluid and surface tension
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Question

A large soap bubble in vacuum is produced by combining N identical soap bubbles, each of radius 2 mm. The final bubble radius is 10 mm. The process is isothermal and no gas is lost. Find N.

G1 Physics · Accepted Answer

For identical soap bubbles combining isothermally in vacuum, R(final)² = N r². Therefore, N = R(final)²/r². Substitute: R(final) = 10 mm, r = 2 mm. Hence, N = 10²/2² = 100/4 = 25. Therefore, N = 25.