Page 127 - text book form physics kssm 2020

Chapter 4
Heat
Results:

Table 4.1
Temperature of Temperature of
Time, t / s thermometer A / °C thermometer B / °C

0

30.0

60.0

Discussion:
1. Why is beaker A wrapped with tissue paper?
2. Describe the changes in temperature of the hot water and tap water.
3. What causes the changes in temperature?

When two objects are in thermal contact, the temperature of the hot object will drop
while the temperature of the cold object will rise until the temperature of both objects become
the same. Net heat transfer between the two objects becomes zero. Both objects are said to be in
thermal equilibrium. Figure 4.2 explains the fl ow of heat between two objects in thermal contact
until thermal equilibrium is reached.
100 100
Heat
80 80 Hot object, P is in thermal contact with cold
60 P Q 60
40 40 object, Q. Th e rate of heat transfer from P to
20 Heat 20 Q is higher than the rate of heat transfer from
0 0 Q to P.

100 100
80 Heat 80 Th ere is a net transfer of heat from P to Q.
60 60
P Q Th erefore, temperature of P drops and
40 40
Heat temperature of Q rises.
20 20
0 0

Temperature of P and temperature of Q become
100 100 the same. Th e rate of heat transfer from P to
80 Heat 80
60 60 Q is the same as the rate of heat transfer from
P Q
40 40 Q to P. Net heat transfer between P and Q
20 Heat 20 becomes zero. P and Q are in a state of thermal
0 0 equilibrium.

Figure 4.2 Flow of heat energy and thermal equilibrium
121
4.1.1 121
4.1.1