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⚛️ Physics  ·  Mechanical Properties of Fluids  ·  NEET & JEE

A gas bubble rises from the bottom of a lake (depth 10 m). When it reaches the surface, its volume:

Answer: Doubles (pressure halves).

  • A Doubles (pressure halves)
  • B Stays the same as generally observed
  • C Quadruples in typical laboratory settings
  • D Halves under usual circumstances

Correct answer: A. Doubles (pressure halves)

Explanation: At 10 m depth, pressure ≈ 2 atm. At surface, 1 atm. By Boyle's law: PV = constant. V<sub>surface</sub> = 2 × V<sub>depth</sub>. Volume doubles.

Continuity Equation: Narrow Pipe → Faster FlowA₁, v₁ (wide, slow)A₂, v₂ (narrow, fast)A₁v₁ = A₂v₂ (continuity)Smaller area → higher speed → (by Bernoulli) LOWER pressure

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.

Read the full Mechanical Properties of Fluids notes →