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Concepts Of Physics MCQ Edition [Volume 1]PhysicsFluid Mechanics

Let P₁ denote the pressure at the surface of the mercury inside a barometer tube, while P₂ represents the pressure at the mercury surface in the cup.

Options

  1. AP₁ = 0 , P₂ = atmospheric pressure
  2. BP₁ = atmospheric pressure, P₂ = 0
  3. CP₁ = P₂ = atmospheric pressure
  4. DP₁ = P₂ = 0

Correct answer

A. P₁ = 0 , P₂ = atmospheric pressure

Step-by-step solution

In a mercury barometer, the space above the mercury column inside the closed tube is a vacuum (known as Torricellian vacuum). Therefore, the pressure at the surface of the mercury inside the tube is zero, giving P₁ = 0 . The surface of the mercury in the cup is open and exposed to the atmosphere. Therefore, the pressure at this surface is equal to the atmospheric pressure, giving P₂ = atmospheric pressure.

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