Final answer:
Relative humidity represents the ratio of the current amount of water vapor in the air to the maximum possible at saturation, expressed as a percentage. It is temperature dependent, with warmer air capable of holding more water vapor. The formula for percent relative humidity is the vapor density divided by the saturation vapor density, multiplied by 100.
Step-by-step explanation:
Definition of Relative Humidity
Relative humidity is defined as the percentage that represents the current vapor density in the air compared to the maximum vapor density at which the air would be saturated. The formula to calculate percent relative humidity is:
percent relative humidity = (vapor density / saturation vapor density) x 100
At 100% relative humidity, the air is fully saturated, meaning that it cannot hold any additional water vapor and this inhibits evaporation. Factors such as air temperature greatly influence relative humidity; warmer air can hold more water vapor than cooler air. This concept explains why blowing hot air is more effective for drying as it increases the evaporation rate due to higher temperature and vapor capacity.
When the air temperature cools in the evening, relative humidity increases, possibly reaching the dew point, and fog can form due to condensation if the water droplets are small enough to remain suspended.