More Questions from Thermodynamics

Standard atmosphere equivalences at mean sea level Select the correct consolidated statement for the standard atmospheric pressure at sea level (International Standard Atmosphere).

Mechanical Engineering Thermodynamics Difficulty: Easy
Choose an option
  • A
    1.013 bar
  • B
    760 mm of Hg
  • C
    1013 × 10^2 N/m^2
  • D
    all of these
  • E
    1.013 × 10^6 N/m^2

Answer

Correct Answer: all of these

Explanation

Introduction / Context:Engineering calculations often require converting standard atmospheric pressure between multiple unit systems. Being fluent with these equivalences avoids mistakes in sizing pumps, compressors, and instrumentation calibrations.

Given Data / Assumptions:

  • Standard atmosphere (mean sea level): approximately 101325 Pa.
  • Mercury column at 0°C has density supporting 760 mm at 1 atm.
  • Bar is a convenient non-SI metric unit used in practice.

Concept / Approach:

Key exact or conventional values used in engineering: 1 atm ≈ 101325 N/m^2 (Pa) ≈ 1.013 × 10^5 N/m^2. This equals approximately 1.013 bar (since 1 bar = 10^5 Pa) and corresponds to a mercury column of 760 mm under standard conditions. Therefore, the grouped option stating “all of these” is correct. Note that 1.013 × 10^6 N/m^2 would be 10.13 bar, which is not standard atmospheric pressure.

Step-by-Step Solution:

Recognize 1 atm ≈ 101325 Pa = 1.013 × 10^5 N/m^2.Convert to bar: 101325 Pa ÷ 10^5 Pa/bar ≈ 1.013 bar.Recall barometric equivalence: 760 mm Hg at 0°C ≈ 1 atm.

Verification / Alternative check:

Instrument calibration tables and ISO/ISA standards list these same equivalences, validating the consolidated choice.

Why Other Options Are Wrong:

1.013 × 10^6 N/m^2: Ten times larger than 1 atm.

Common Pitfalls:

Mixing bar (10^5 Pa) with Pascal and kiloPascal; remember 1 bar = 100 kPa (exact by definition).

Final Answer:

all of these

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