Answer: 8πR² T.
- A 8πR² T
- B 2πR² T
- C 4πR² T
- D 16πR² T
Correct answer: A. 8πR² T
Explanation: Work = surface tension × increase in surface area = T × 2 × 4πR² = 8πR² T. The factor 2 is because a soap bubble has two surfaces.
Since the same volume of fluid must pass every cross-section per second (continuity), the fluid speeds up where the pipe narrows; Bernoulli's equation then says this faster-moving fluid has lower pressure - the principle behind a venturi meter and an aircraft wing's lift.
Concept context
Pressure, buoyancy, Bernoulli equation, viscosity, and surface tension.