A bottle of perfume is opened in one corner of a closed room with no fan.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A bottle of perfume is opened in one corner of a closed room with no fan. A minute later, a person in the opposite corner can smell it.
- Explain why.
- On a cold winter day the smell takes longer to arrive. Why?
- Why is the smell strongest close to the bottle?
Need a reminder? The key ideaShow
The particles of matter are always moving. Diffusion is the spreading of one substance through another by itself, because of this motion. It is fastest in gases and faster at a higher temperature, because heated particles move faster.
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) Particles of the perfume leave the bottle as a gas. They are always moving, and they spread among the moving particles of the air by diffusion until they reach the far corner.
Step 2. (b) In cold air the particles have less energy and move more slowly, so diffusion is slower.
Step 3. (c) Diffusion goes from where there are many particles to where there are few. Near the bottle there are the most particles of perfume, so the smell is strongest there.
Answer: The particles move and spread by diffusion; more slowly when it is cold; and they are most crowded near the bottle.
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