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What is atmospheric pressure ? Define standard atmospheric pressure. |
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Answer» The Earth’s surface is covered with a layer of atmosphere, with more than 99% of the atmosphere lying within 31 km of the surface. The weight of the atmosphere exerts a downward thrust on any surface lying within it. This gives rise to atmospheric pressure. The atmospheric pressure at any height above the Earth’s surface is the weight of a column of air of unit cross section from that altitude to the top of the atmosphere. Definition : Standard atmospheric pressure, or one atmosphere of pressure, is defined as the pressure equivalent of a column of mercury that is exactly 0.7600 m in height at 0 °C. We can calculate this equivalent pressure in SI unit by using the density of mercury ρ = 13.6 × 103 kg/m3 and g = 9.80 m/s2 . 1 atm = (0.76 m) . (13.6 × 103 kg/m3) . (9.80 m/s2) = 1.013 × 105 Pa = 101.3 kPa [Note : 1000 mbar = 100 kPa. Therefore, 1 atm = 1013 mbar.] |
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