Mean free path doubles when:
ADensity doubles
BPressure halves at constant T (or density halves)
CT doubles at const V
DRandom
Answer & Solution
Correct answer: B. Pressure halves at constant T (or density halves)
λ ∝ 1/n (number density). Halving P at const T halves n → doubles λ. Hence high-vacuum: extremely long λ (atoms travel meters between collisions).
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