Relative Humidity Evaporation What is relative humidity The
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Relative Humidity (Evaporation)
What is relative humidity? • The percentage of moisture the air holds compared to the amount of moisture it could hold at a certain temperature
How does moisture enter the air? • Through evaporation • Oceans are the largest source of moisture For the planet.
What temperatures hold more water vapor? • Higher temperatures hold more water vapor because the “air expands” allowing more room for water vapor.
What device is used to measure relative humidity? • A sling psychrometer, it contains a dry bulb and a wet bulb temperature
What is the relationship between the wet bulb and the dry bulb and the amount of humidity in the air? • As the difference of the wet bulb and dry bulb increases, the humidity decreases, and vice versa. • If the wet bulb and dry bulb are close together, the humidity is high.
What are three factors that affect the rate of evaporation? • Energy- temperature – the higher the • • temperature, the higher the rate of evaporation Surface area- as surface area increases, the rate of evaporation increases. Moisture content of the air- As moisture content (RH) of the air decreases, the rate of evaporation increases.
Cooling the Surface…. • Because water needs energy (heat) to evaporate into a gas, it gets this energy from the surface it was on. • Once the water leaves, it takes this energy (heat) with it, leaving the surface feeling cooler. • This is why humans sweat. Sweating makes us feel cooler in temperature. • This why the temp of wet bulb is always colder.
