Page 162 - Physics

Physics for Secondary Schools

Pointer
Metal spring Chain

Levers

Partially
evacuated
box

(a) Internal appearance (b) External appearance

Figure 7.31: Aneroid barometer

The aneroid cell is prevented from Siphon
collapsing under the pressure of A siphon is a continuous tube that allows liquid
the atmosphere by a strong spring. to drain from a reservoir through an intermediate
The spring is attached through a set point that is higher than the reservoir. The liquid
of levers to a pointer that indicates can fl ow without pumping because of pressure
the pressure on a calibrated scale, difference. To do this the end of the long arm has

as shown in Figure 7.31 (b). Even to be lower than the surface of the liquid in the
though it contains no mercury, the reservoir as shown in Figure 7.32.
pressure is still measured in units
of mmHg. Atmospheric Water direction
pressure
Task 7.4 Siphon

Discuss why it is advantageous
to use the aneroid barometre Water Long arm
instead of the Fortin barometer. Short arm
Table
Common devices utilizing Beaker
atmospheric pressure
There are a variety of common and

even simple devices that make use Water
of atmospheric pressure. These
include drinking straws, cupping Figure 7.32: The siphon principle
therapies, siphons, bicycle pumps,
lift pumps, force pumps, vacuum The liquid rises in the tube because it is pushed by
cleaners and syringes. atmospheric pressure. The atmospheric pressure
acts on both ends of the siphon but the long arm

156
Student’s Book Form One

Physics Form 1 Final.indd 156 16/10/2024 20:57