Humidity, evaporation, and condensation

Dry air has less water vapour so it can take more moisture. This is also why clothes dry faster in dry air.

Evaporation needs latent heat which is taken from the body. Therefore evaporation of sweat gives cooling.

Under a clear sky the ground loses heat rapidly and cools. Water vapour can condense as dew on the cool surface.

Dust smoke and salt particles can act as condensation nuclei. Water vapour forms droplets around them.

Evaporation from water surfaces and transpiration from plants together are called evapotranspiration. It is important in the water cycle.

Evaporation is faster in warm and dry air. Drying clothes is a daily example of evaporation.

When temperature rises air capacity increases and the same vapour becomes a lower percentage. Thus relative humidity may fall on a warm afternoon.

A hygrometer is used to measure humidity of air. In instrument questions match the name with its function.

Water vapour is linked with clouds condensation and rainfall. Therefore it is a key element in meteorology.

Saturated air holds moisture up to its maximum capacity. Extra moisture may come out through condensation.

Strong wind removes the moist layer near the water surface. This brings drier air and increases evaporation.

Relative humidity is the percentage ratio of actual vapour pressure to saturation vapour pressure. Always understand the percent part in the formula.

When saturated air cools further extra water vapour condenses. This is the basis of clouds dew and fog.

During the day, desert temperatures are very high, giving water molecules more energy to escape as vapour. The air is also low in humidity, so it can accept more water vapour; therefore, evaporation is rapid. Low temperature and high humidity would have the opposite effect and reduce evaporation. Exam tip: evaporation increases with higher temperature and lower relative humidity.

Condensation forms cloud droplets and when they grow larger rainfall becomes possible. Understand cloud formation before precipitation.

Wind and clouds can reduce effective surface cooling. Calm and clear nights are more favourable for dew.

During monsoon higher moisture slows evaporation of sweat. Therefore sultriness is felt more.

High temperature increases air moisture holding capacity. So relative humidity may be moderate despite high actual moisture.

Oceans lakes rivers and moist soil are common sources of evaporation. Remember water surfaces as main sources.

Direct change of water vapour into solid ice is called deposition. It can be important in cold clouds.