The statement about air: The specific volume of air at 80° dry bulb and 55° dew point is approximately 13.6 cubic feet per pound.

• A. True
• B. False
• C. Depends on humidity
• D. Only at sea level

Answer: (B)

Specific volume is not fixed by dry-bulb and dew-point alone; it depends on both humidity and pressure. The pair “80° dry bulb” and “55° dew point” tells you how hot the air is and how moist it is, but it doesn’t fix the pressure. At different pressures the same temperature and moisture content give you different densities, and thus different specific volumes. Therefore pinning it to a single number like 13.6 cubic feet per pound isn’t reliable for those conditions, so the statement isn’t generally true. In psychrometric terms, you’d need the pressure (and thus the density) to determine the exact value, not just the temperatures implied by the dry-bulb and dew point.