Final answer:
The lower the relative humidity, the larger the difference between the actual air temperature and the dew point. Low RH means air can hold more water vapor before reaching saturation, resulting in a larger temperature difference.
Step-by-step explanation:
The question pertains to the relationship between relative humidity (RH) and the difference between the actual air temperature and the dew point. The lower the relative humidity (RH), the larger the difference between the actual air temperature and the dew point. When the RH is low, the air can hold more water vapor before it becomes saturated, which is when the actual air temperature equals the dew point temperature. Conversely, as RH increases, indicating more moisture in the air, the difference between the two temperatures decreases. For example, on hot, dry days, the evaporation of sweat from the skin cools the body effectively because the RH is typically lower, leading to a larger difference between the air temperature and the dew point. However, on humid days the concentration of water in the atmosphere is higher (increased RH), which reduces the evaporation rate from the skin's surface due to a smaller difference in water vapor pressure. This illustrates the broader principle that increased humidity leads to reduced evaporation rates due to the decreased difference in water vapor pressure between the leaf (or skin) and the atmosphere.