Maharashtra BoardEnglish MediumSTD 12 SciencePhysicsMechanical Properties of Fluids4 Marks
Question
What is atmospheric pressure ? Define standard atmospheric pressure.
✓
Answer
The Earth's surface is covered with a layer of atmosphere, with more than $99 \%$ of the atmosphere lying within $31 \mathrm{~km}$ 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 $0.7600 \mathrm{~m}$ in height at $0^{\circ} \mathrm{C}$. We can calculate this equivalent pressure in SI unit by using the density of mercury $ \begin{aligned} & \rho=13.6 \times 10^3 \mathrm{~kg} / \mathrm{m}^3 \text { and } \mathrm{g}=9.80 \mathrm{~m} / \mathrm{s}^2 . \\ & 1 \mathrm{~atm}=(0.76 \mathrm{~m}) \cdot\left(13.6 \times 10^3 \mathrm{~kg} / \mathrm{m}^3\right) \cdot\left(9.80 \mathrm{~m} / \mathrm{s}^2\right) \\ & =1.013 \times 10^5 \mathrm{~Pa}=101.3 \mathrm{kPa} \end{aligned} $ [Note : $1000 \mathrm{mbar}=100 \mathrm{kPa}$. Therefore, $1 \mathrm{~atm}=1013 \mathrm{mbar}$.]
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.