Page 169 - text book form physics kssm 2020

Chapter 4
Heat
Example 3

Initial pressure and temperature of air in the tyre of a car are 210 kPa and 25°C respectively.
Aft er a journey, the air pressure in the tyre is 240 kPa. Calculate the temperature of the air in
the tyre in °C.

Solution:
Assume the volume of the tyre does not change. Gay-Lussac’s Law is used.

P = 210 kPa P 1 P 2
1
P = 240 kPa T 1 = T 2
2
T = 25°C + 273 210 240
1
= 298 K 298 = T 2
T = Final temperature of air 240 × 298
2
T =
2
210
= 340.6 K
Final temperature of air = 340.6 – 273
= 67.6°C

Formative Practice 4.4
4.4
1. State the physical quantities that are constant in Boyle’s Law, Charles’ Law and
Gay-Lussac’s Law.

3
2. A syringe contains 50 cm of air at a pressure of 110 kPa. Th e end of the syringe is closed
3
and its piston slowly pushed until the volume of air becomes 20 cm . What is the pressure
of the compressed air?
3
3. An air bubble trapped under a leaf in a lake has a volume of 1.60 cm at a temperature of
38°C. Calculate the volume of the bubble if the temperature of the water in the lake drops
to 26°C.

4. Pressure in a gas cylinder is 175 kPa at a temperature of 27°C. Heat from a nearby furnace
causes the gas pressure to increase to 300 kPa. What is the temperature of the gas inside
the cylinder?

5. Figure 4.35 shows an apparatus set up to Thermometer
study the relationship between pressure and Round-
bottom
temperature for air inside a round-bottom fl ask. flask Rubber tube
(a) Identify four aspects in the apparatus set Ice
up that can jeopardise the accuracy Water
of the results of the experiment. Retort Wire Pressure gauge
stand gauze
(b) Suggest modifi cations to improve Bunsen Tripod
the set up. burner
stand

Figure 4.35
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4.4.5 163
4.4.5