Page 160 - Physics
P. 160
Physics for Secondary Schools
Questions Acti vity 7.6
(a) What happens to the can?
(b) Explain your observation. Aim: Constructing a simple
mercury barometer.
Steam emerging from boiling water drives Materials: Thick-walled glass tube
out air from the can. When the can is about 1 m long sealed
cooled by cold water the steam condenses, at one end, mercury and
leaving a partial vacuum inside the can. glass trough
Consequently, the higher atmospheric
pressure outside the can crush it inwards.
Vaccuum
Measurement of atmospheric pressure
Atmospheric pressure is commonly
measured by using a barometer. In this Mercury
section, you will learn three types of
barometers, namely simple barometer,
Fortin barometre and aneroid barometer. Figure 7.29
Simple barometre Procedures
A simple barometre is the most fundamental 1. Fill the glass tube with mercury to
of the other types of barometers. The almost the top of the tube.
barometric liquid used is mercury. A simple 2. Ensure that no air bubbles are trapped
barometre consists of a hard glass tube on the wall of the glass tube. This is
closed at one end and a glass trough fi lled done by closing the open end with a
with mercury as shown in Figure 7.28. fi nger and inverting it several times.
3. Now, fi ll the tube completely with
Vacuum
mercury.
4. With a fi nger closing the open end,
Glass tube invert the tube into the trough of
mercury. When the fi nger covering
0.76 m Atmospheric the open end is removed, the mercury
pressre presses
on mercury is seen to settle to a height of about
760 mmHg.
Mercury Note: Mercury should be handled with
Glass trough care to avoid poisoning.
Questions
Figure 7.28: A simple barometer
(a) Why is it necessary to close the
Atmospheric pressure pushes mercury to open end of the tube when making
a height of 76 cm at mean sea level. a simple mercury barometer?
154
Student’s Book Form One
Physics Form 1 Final.indd 154 16/10/2024 20:57
