MediumChemistryHigh School (9–10)GeneralStates of Matter › Evaporation and CoolingConceptualBoard Exam
Four plates hold the same amount of water…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Four plates hold the same amount of water. Plate P is wide, in the sun, with no wind. Plate Q is wide, in the sun, with a fan blowing over it. Plate R is narrow, in the sun, with no wind. Plate S is wide, in the sun, with no wind, but covered with a loose lid.
- Which plate dries first?
- Which dries faster, P or R?
- Which dries faster, P or S, and why?
Need a reminder? The key ideaShow
Evaporation is the change of a liquid into a gas at its surface, at any temperature. It is faster with a larger surface, a higher temperature, a lower humidity and more wind. Boiling happens all through the liquid, at the boiling point, with bubbles.
The worked solution
Have you tried it?
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) Q has a wide surface, the warmth of the sun and moving air, so it dries first.
Step 2. (b) P and R differ only in the surface. P is wider, so P dries faster.
Step 3. (c) P and S differ only in the lid. Under the lid the vapour cannot get away, so the air above the water becomes humid and evaporation slows down. P dries faster.
Answer: (a) Q. (b) P. (c) P.
Check. Changing one thing at a time is a fair test: it shows which factor made the difference.
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