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Physics for Secondary Schools
The pressure difference at sea level and our body and why does yawning
this altitude is 1−0.79 = 0.21 atm help to solve the issue?
3. Does atmospheric pressure add to the
Therefore, the cabin pressure should be gas pressure in a rigid tank of gas?
given a pressurization of 0.21 atm In a toy balloon? When, in general,
does atmospheric pressure not affect
Example 7.8 the total pressure in a fl uid?
A mercury barometre in a physics
laboratory reads 732 mmHg. Calculate Evidence for the existence of
the atmospheric pressure in Pascal. atmospheric pressure
The existence of atmospheric pressure
(Given density of mercury, can be verifi ed experimentally using the
ρ = 1.36 × 10 kg/m and acceleration following apparatus:
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3
due to gravitational g = 9.8 N/kg) 1. Magdeburg hemispheres.
2. Water covered with cardboard.
Solution:
Atmospheric pressure in the laboratory, 3. Crushing can.
P = hρg Magdeburg hemisphere
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P = 0.732m
= 0.732 m × 13600 kg/m × 9.8 N/kg Magdeburg hemispheres are two half-
spheres of equal size joined to form an air
P = 9.7561×10 Pa or 97 561 Pa
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tight sphere. Placing them together traps air
between them. This air is merely trapped
Exercise 7.2 and not compressed, thus the pressure
1. (a) Can high altitude cause inside is the same as the pressure of the
diffi culty in breathing? Why? atmosphere outside the spheres as shown
by arrows in Figure 7.25 (a). In this case,
(b) At a given place, a mercury one can pull the spheres apart with nearly
barometre records a pressure of no resistance.
0.50 m of Hg. If mercury in the
barometre is replaced by water.
What would be the height of
the water column? Take R.D.
of mercury = 13.6.
2. Explain why: (a) The air pressure (b) The air pressure
(a) There is a possibility of nose inside and outside inside the hemisphere
bleeding at high altitude. the hemisphere is is lower than the
(b) Our ears pop when going on balanced outside
mountain. What is going on in Figure 7.25: Action of Magdeburg hemisphere
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Student’s Book Form One
Physics Form 1 Final.indd 152 16/10/2024 20:57
