Air at a temperature of 20°C and 750 mm Hg pressure has a relative humidity of 80%. What is its percentage humidity? Vapour pressure of water at 20°C is 17.5 mm Hg?
Correct answer: C. 79.62
- A. 80.38
- B. 80
- C. 79.62
- D. 78.51
Explanation
Relative humidity gives a vapour partial pressure of 0.80 × 17.5 = 14 mm Hg. Correcting the vapour-to-dry-air ratio for total pressure gives percentage humidity = [14/(750−14)]/[17.5/(750−17.5)] × 100 = 79.62%.
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