What is the standard atmospheric pressure at sea level?
Try it first: pick an option, then read the explanation.
Asked in SSC JE 09/10/2023 (10am-12pm)
Detailed Explanation
Standard atmospheric pressure (1 atm) represents the mean sea-level pressure defined internationally for scientific and engineering calculations.
Standard sea-level atmospheric pressure equivalents:
\[ 1\text{ atm} = 101{,}325\text{ Pa} = 101.325\text{ kPa} \]
Since \(1\text{ bar} = 10^5\text{ Pa} = 100\text{ kPa}\):
\[ p_{\text{atm}} = \frac{101{,}325}{10^5}\text{ bar} = 1.01325\text{ bar} \approx 1.013\text{ bar} \]
Why “1.013 bar” Is Correct
1 standard atmosphere equals 101.325 kPa, which converts to 1.01325 bar (rounded to 1.013 bar).
Why the Other Options Are Wrong
- A. 1.5 bar: 1.5 bar is 50% higher than atmospheric pressure.
- C. 1.3 bar: 1.3 bar is roughly 30% above standard sea-level pressure.
- D. 1013 mmHg: Standard pressure is 760 mmHg, not 1013 mmHg (1013 is the value in millibars or hPa).
Key Point
1 atm = 101.325 kPa = 1.01325 bar = 760 mm Hg = 10.3 m of water.
Key Concepts for Students
- 1 bar = 10⁵ N/m² = 100 kPa.
- In terms of liquid columns: 760 mm of mercury (density 13,600 kg/m³) or 10.33 m of water.
- Barometric pressure varies locally with weather systems and altitude.
Practice more: this is question 15 in Properties of Fluid MCQs – Part 1. Try the whole set and check every answer instantly.