On two days the temperature is 35 °C. On the first day the relative humidity is 30 %, and on the…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
On two days the temperature is . On the first day the relative humidity is , and on the second it is .
- On which day do we feel hotter? Explain with evaporation.
- On which day would a desert cooler work better?
Need a reminder? The key ideaShow
Humidity is the water vapour in the air. Humid air takes in little more vapour, so sweat and wet clothes dry slowly, and we feel hotter. Warm air can hold more vapour than cool air.
The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) At the air is dry and takes in vapour easily, so sweat evaporates fast and takes heat from the body. At the air is nearly full, so sweat evaporates slowly and stays on the skin. We feel hotter on the humid day.
Step 2. (b) The cooler needs water to evaporate from its pads. That happens fast in dry air, so the cooler works better on the dry day, at .
Answer: (a) The day with humidity. (b) The day with humidity.
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