Dew Point and Humidity

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

1. $60\%$
2. $51\%$
3. $35\%$
4. $75\%$

Q. The weather report reads,
“Temperature: $20{}^{\circ }C$,
Relative humidity: $100\%$”.
What is the dew point?

1. Less than ${20}^{\circ }C$
2. ${20}^{\circ }C$
3. More than ${20}^{\circ }C$
4. Can’t be said.

Q. The temperature and the dew point in an open room are $20{}^{\circ }C$ and $10{}^{\circ }C$. If the room temperature drops to $15{}^{\circ }C$, what will be the new dew point?

1. ${10}^{\circ }C$
2. ${11}^{\circ }C$
3. ${15}^{\circ }C$
4. ${20}^{\circ }C$

Q. In some areas, people sweat a lot because the relative humidity is higher as compared to other areas.

1. True
2. False

Q. Dew point can be reached by increasing the temperature of the system.

1. True
2. False

Q.

A glass contains some water at room temperature ${20}^0$C. Refrigerated water is added to it slowly. When the temperature of the glass reaches ${10}^0$ C, small droplets condense on the outer surface. Calculate the relative humidity in the room. The boiling point of water at a pressure of 17.5 mm of mercury is ${20}^0$ C and at 8.9 mm of mercury it is ${10}^0$ C.

Q.

The temperature and the dew point in an open room are ${20}^0$C and ${10}^0$C. If the room temperature drops to ${15}^0$C, what will be the new dew point ?

Q.

The weather report reads, "Temperature 20^0 C : Relative humidity 100 %". What is the dew point ?

Q.

On a winter day, the outside temperature is $0^0$ C and relative humidity 40 %. The air from outside comes into a room and is heated to ${20}^0$ C. What is the relative humidity in the room ? The saturation vapour pressure at $0^0$ C is 4.6 mm of mercury and at ${20}^0$ C it is 18 mm of mercury.

Q.

A bucket full of water is placed in a room at ${15}^0$ C with initial relative humidity 40 %. The volume of the room is 50 $m^3$. (a) How much water will evaporate ? (b) If the room temperature is increased by $5^0$ C, how much more water will evaporate ? The saturation vapour pressure of water at ${15}^0$ C and ${20}^0$ C are 1.6 kPa and 2.4 kPa respectively.