AMUEEE Thermodynamics & Kinetic Theory — practice questions — page 2

Explore 32 free Thermodynamics & Kinetic Theory questions in AMUEEE Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Thermodynamics & Kinetic Theory questions and exercises with answers

Showing questions 31–32 of 32.

If the mean free path of N₂ at 1 atm is ~80 nm, what is it at 0.01 atm (same T)?Read the answer and worked solution →The number of moles of oxygen ($O_2$) gas in a vessel of volume 1 L at STP (273.15 K, 1.013 × 10⁵ Pa) is approximately:Read the answer and worked solution →

Worked practice questions

If the mean free path of N₂ at 1 atm is ~80 nm, what is it at 0.01 atm (same T)?

~ 8 nm
~ 80 nm
~ 800 nm
~ 8 μm (mean free path ∝ 1/P)

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Correct answer: D. ~ 8 μm (mean free path ∝ 1/P)

λ ∝ T/P. Reducing P by 100× increases λ by 100×: 80 nm × 100 = 8000 nm = 8 μm. (Why vacuum coating works at low pressure — gas molecules don't collide before reaching the substrate.)

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The number of moles of oxygen ($O_2$) gas in a vessel of volume 1 L at STP (273.15 K, 1.013 × 10⁵ Pa) is approximately:

~ 0.045 mol
~ 0.045 g
~ 1.0 mol
~ 22.4 mol

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Correct answer: A. ~ 0.045 mol

$n = PV/(RT) = (1.013\times10^5)(10^{-3})/(8.314\times273.15) = 101.3/2270.6 \approx 0.0446$ mol. Equivalently, 22.4 L = 1 mol at STP, so 1 L ≈ 1/22.4 = 0.0446 mol.