physics-form-4-chapter-4.pdf - Heat Heat is closely related...

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H eat is closely related to human life. Topics in this theme discuss concepts and laws related to heat energy. We will investigate the aspects of changes in phases of matter, especially changes in the properties of gas. Three gas laws, Boyle’s Law, Charles’ Law and Gay-Lussac’s (pressure) Law, will also be introduced. Heat 117
Let’s Study 4.1 Thermal Equilibrium 4.2 Speci fi c Heat Capacity 4.3 Speci fi c Latent Heat 4.4 Gas Laws Why is water suitable to be used as a cooling agent?What is the importance of specific heat capacity of a substance?What influences the behaviour of gas molecules?Heat4 118
Kitchen is where a lot of the concepts related to heat energy can be applied. When we heat up water in a kettle, the rate of increase in water temperature depends on the quantity of water heated. When the water boils, its temperature will no longer increase. When the same quantity of oil and water are heated separately at the same time, oil will be hotter first. All these examples involve the relationship and interaction between physical properties of matter such as temperature, pressure, volume and heat. Applications of the concept of heat have greatly helped our daily life. Video on application of physics concepts in the kitchen Learning Standards and List of Formulae Page Information 119
Thermal Equilibrium 4.1 Observe Photograph 4.1. When a cold metal spoon is put into a cup of hot coffee, the spoon and the coffee are said to be in thermal contact because heat energy can be transferred between the two bodies. How can the metal spoon cool down the hot coffee? What is the final condition of the spoon and the coffee? Photograph 4.1 A cold metal spoon in a cup of hot coffee A ctivity 4.1 Aim: To show thermal equilibrium between two bodies in thermal contact Apparatus: Two retort stands, two thermometers, 250 m l beaker labelled A , 50 m l beaker labelled B , measuring cylinder and stopwatch Materials: 50°C hot water, tap water and tissue paper Instructions: 1. Wrap beaker A with tissue and fi ll it with 150 m l of tap water. 2. Fill 40 m l of 50°C hot water into beaker B . 3. Place beaker B into beaker A . Then, place thermometer A and thermometer B into beaker A and beaker B respectively as shown in Figure 4.1. Retort stand Tissue paper Hot water Thermometer A Thermometer B Tap water Beaker A Beaker B Figure 4.1 4. Record the readings of thermometer A and thermometer B every 30 s until the readings of both thermometers are the same. (This activity can normally be carried out in fi ve minutes) 120 4.1.1
Results: Table 4.1 Time, t / s Temperature of thermometer A / °C Temperature of thermometer B / °C 0 30.0 60.0 Discussion:

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