Page 66 - Physics Form 5 KSSM_Neat

2.3 Gas Pressure

Manometer

Photograph 2.3 shows a manometer which consists of a glass U-tube
containing coloured water. This apparatus is used to measure gas
KEMENTERIAN PENDIDIKAN MALAYSIA
pressure. Figure 2.17 shows a manometer before and after it is
connected to a gas supply.

Photograph 2.3 Manometer
(a) Before connecting to a
gas supply (b) After connecting to a gas supply

P P P
atm atm atm

P
gas h

Water

A B
Gas

Figure 2.17 Water manometer before and after connecting to a gas supply

Pressure at A = gas pressure, P gas
Pressure at B = pressure due to water column h + atmospheric pressure
= h cm H O + P
2 atm
Point A and point B are at the same level, therefore
Pressure at A = pressure at B
P = h cm H O + P atm
gas
2
The height, h of the water column represents the difference between the gas pressure and
atmospheric pressure. Let us carry out Activity 2.5 to understand more about gas pressure in a
container by using a water manometer.

56 LS 2.3.1