Air is about 20.95 per cent oxygen at every height…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Air is about per cent oxygen at every height. In a standard atmosphere the air pressure is kPa at sea level and kPa at a height of m.
- What is the pressure of oxygen at sea level, in kPa?
- What is the pressure of oxygen at m?
- What per cent of the sea level value is it at m?
Need a reminder? The key ideaShow
A ball of radius has the surface area and the volume . So its surface for each unit of volume is . Allen's rule: shorter ears and limbs in cold climates. At high altitude, the body makes more red cells, haemoglobin binds oxygen less, and breathing is 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.
Given. Oxygen: of the air. Pressures: kPa and kPa.
Plan. Multiply each air pressure by , then compare.
Step 1. (a) kPa.
Step 2. (b) kPa.
Step 3. (c) , so about .
Answer: kPa; kPa; .
Check. The share of oxygen is the same at both heights, so the share of the pressure is the same as for the air, .
Watch out. The air does not have less oxygen in each litre of gas. The lower pressure means that each breath has fewer molecules in it.
Source. International Standard Atmosphere, with 20.95 per cent oxygen by volume in dry air.
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