A glass contains some water at room temperature 20°C. Refrigerated water is added to it slowly. When the temperature of the glass reaches 10°C, small droplets condense on the outer surface. Calculate the relative humidity in the room. The boiling pointing of water at a pressure of 17.5 mm of mercury is 20°C and at 8.9 mm of mercury it is 10°C.

Question

Philoid · Accepted Answer

Given

Temperature of water=20

Droplets starts to form at 10.

Therefore, dew point is =10. This is because at dew point vapor pressure becomes saturated vapor pressure and after that air cannot hold more moisture and will start to condense.

At boiling point, saturation vapor pressure becomes equals to atmospheric pressure.

So, given that,

At temperature 20 pressure is 17.5mm of Hg.

SVP (saturation vapor pressure) at 20 = 17.5mm of Hg

SVP at dew point i.e. 10 =8.9mm of Hg

Now relation between relative humidity and dew point is

Relative humidity in the room is 51%.