Concepts Of Physics MCQ Edition [Volume 2]PhysicsKinetic Theory of Gases
A glass holds some water at a room temperature of 20^ C . Refrigerated water is slowly added to it. Once the glass temperature drops to 10^ C , tiny droplets begin to condense on its outer surface. Determine the relative humidity in the room. The boiling point of water is 20^ C at a pressure of 17.5 mm of mercury, and 10^ C at 8.9 mm of mercury.
Options
- A50 %
- B57 %
- C45 %
- D51 %
Correct answer
D. 51 %
Step-by-step solution
The dew point of the air in the room is the temperature at which condensation begins, which is 10^ C . The partial pressure of water vapor in the room is equal to the saturated vapor pressure at the dew point. Since the boiling point of water is 10^ C at 8.9 mm of Hg, the saturated vapor pressure at 10^ C is 8.9 mm of Hg. Similarly, the saturated vapor pressure at the room temperature of 20^ C is 17.5 mm of Hg. Relative humidity is given by the ratio of the partial pressure of water vapor to the saturated vapor pre