The document discusses atmospheric pressure and different ways of measuring it. It explains that atmospheric pressure decreases with altitude due to lower air density and temperature. Standard atmospheric pressure at sea level is approximately 760 mmHg or 101,325 Pascals. The document also describes various instruments used to measure pressure, including mercury barometers, aneroid barometers, and manometers.

1. Atmospheric Pressure and Layers
Lesson 1

2. Atmospheric Pressure

3. Atmospheric Pressure
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4. Drop of Pressure
Drop of Pressure

5. Atmospheric Pressure
Atmospheric pressure is the force
exerted on the Earth’s surface by
air molecules of the atmosphere
per unit area of the surface
Pr
Force
essure
Area

Atmospheric pressure decreases with altitude.
Reason :
1. At a higher altitude, the density of the air is lower.
2. At a higher altitude, the temperature of the air is lower,
hence less collisions.

6. • 760 mm Hg
• Standard Atmospheric
pressure (1 atmosphere)
• 0.76x 13600 x 10 Pa
= 103360 Pa
= 103360 N m-2
• = 1.0336 x 105 Pa
= 1.0336 bar of pressure
• 10.336 m water
Mercury barometer
At sea level, h
= 760 mm
760 mm Hg
1 atm.
105 Pa
105 N m-2
10 m
water
76 cm Hg
1 bar pf
pressure
VARIOUS UNITS OF ATMOSPHERIC
PRESSURE

7. Mercury Barometer
Vdo

8. 760mm Hg = 1.0atm = 101.325kPa = 1013.25 mb
Standard Atmospheric Pressure

9. The reading of a mercury barometer at a
meteorological station is 745 mm mercury. What is
the value of the atmospheric pressure at the
meteorological station in pascal ?
EVALUATION

10. Aneroid Barometer
Aneroid Barometer
vdo

11. Precision Aneroid Barometer
Precision Aneroid Barometer

12. EVALUATION
1. If 10 cm3 of mercury
is added into the
bowl, what happen
to the value of h ?
A > 76 mm
B < 76 mm
C 76 mm
h = 76 mm

13. A P
B P and Q
C Q and R
D P, Q and R
EVALUATION
2. A barometer is placed in an
region where the atmospheric
pressure is 76 mm Hg. Which of
the diagrams shows the correct
level of the mercury.
h = 76 mm
h = 76 mm
vapour
h > 76 mm
P Q R

14. EVALUATION
3. Figure shows a soft toy hung on a suction cup.
The soft toy does not fall to the
floor because the pressure in
A P > Q
B P = Q
C P < Q
D Q = 0

15. The atmospheric pressure is 760
mm Hg and the difference in the
mercury level of a manometer
measuring the pressure of a gas is
20 mm. What is the pressure of
the gas in mm Hg ?
EVALUATION