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Mass, Weight, Density and Pressure

Quick questions on Gas pressure and the mercury barometer explained: O-Level Physics

5short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is the manometer?
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A manometer is a U-shaped tube partly filled with liquid (often mercury or water). One arm connects to the gas supply; the other is open to the atmosphere.
What is the mercury barometer?
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A mercury barometer measures atmospheric pressure. A long tube is filled with mercury and inverted into a dish of mercury. The mercury falls until the column's pressure balances the atmospheric pressure pushing down on the dish, leaving a vacuum at the top. The vertical height of the mercury column then measures atmospheric pressure:
What is q1?
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Explain, in terms of particles, how a gas exerts pressure on its container. [2 marks]
What is q2?
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A mercury column of height 0.70 m0.70\ \text{m} (ρ=13600 kg m3\rho = 13\,600\ \text{kg m}^{-3}, g=10 N kg1g = 10\ \text{N kg}^{-1}) balances the atmosphere. Find the atmospheric pressure. [2 marks]
What is q3?
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State why mercury, not water, is used in a barometer. [2 marks]

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