Ch. 4 Questions for Review

6.) (a) What does the relative humidity represent? (b) When the relative humidity is given, why is it also important to know the air temperature? (c) Explain two ways the relative humidity may be changed. (d) During what part of the day is the relative humidity normally lowest? Normally highest?

(a)

10.) (a) What is the dew-point temperature? (b) How is the difference between dew point and air temperature related to relative humidity

(a) The temperature below which the water droplets begin to condense is known as dew-point. At this temperature the air can hold no water vapor. Dews are formed when air cools to the dew-point temperature. (b) The relative humidity becomes 100% when air temp matches dew-point temp. When RH reaches 100%, the air is not capable of holding any more water vapor. Hence, the water vapor condenses to water droplets and finally forms dew and fog. If it is cooled furthermore, then the frozen dews and the frosts are formed.

13.) List the two primary ways in which fog forms.

1.) one way to form fog is by allowing the air to cool to certainly low temperature that is below dew-point (saturation point). At this temperature the water vapor condenses to form fog. 2.) The other way to form fog is by evaporation. The water that is on the surface of the water bodies gets evaporated and added to air. This leads to increase in the relative humidity. When the RH in the air is 100% and the surface temp is equal or near to dew point, then the air can hold no more humidity. At these conditions the water vapor condenses to form fog.

5.) What does saturation vapor pressure primarily depend on?

Relative humidity is the ratio if the actual amount of water vapor in the air to the amount needed reach saturation. Humidity can make air temperature feel warmer than it is by preventing evaporative cooling and convection. During the winter, people run their furnaces. Most furnaces have a humidifier that adds moisture to the air inside the house preventing the low humidity that occurs from heating the air, and this can make the house feel warmer. At the march equinox the outside usually increases and people no longer run their furnace. This leads to decreased humidity and thus a perceived lower temperature.

2.) How does condensation differ from precipitation?

Water moves in a continuous cycle in the earth and the atmosphere. Evaporation and condensation are two ways water moves. In evaporation, water vapor absorbs radiation from the sun and changes from a liquid to a gas. Small particles of dust can act as condensation nuclei in the air to trigger condensation. When the temperature is colder, water vapor moves more slowly and can stick to the condensation nuclei, forming clouds and precipitation. However, when temperatures are warm, such as a desert, there may be lots of water vapor in the air, but they are moving too fast to stick to the condensation nuclei. Thus, no precipitation forms. The travel agent is correct. There may be a high concentration of water molecules, but due to the heat, there will be no condensation.