Teaching ideas ◆
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In this section, we think about the forces between particle. Show how you can break a thin piece of wood or a stick of chalk. You are separating adjacent particles by overcoming the forces between them. Ask if students can name a material with much stronger forces than chalk (steel, for example). If students have learned about bonding in chemistry, you can bring in these ideas here. Figure 9.8 in the Coursebook shows what happens when a gas condenses, in terms of the particles. At first, they are moving around rapidly so they do not readily stick together. At a lower temperature, they stick and clump together to form a liquid. Go on to consider evaporation in more detail. Now you can bring in ideas about the energy of a particle. Some particles have more energy than others and so can escape more readily; this explains the cooling effect of evaporation. Activity 9.3 will test your students’ ability to devise explanations using the kinetic model. Unfortunately, it is difficult to find marbles that will stick together so we cannot model the intermolecular forces. However, students can answer the questions using the marbles to illustrate their ideas. Coursebook questions 9.11 to 9.13 can be used to sum this up.
Common misunderstandings and misconceptions ◆
As before, ensure that students do not have the idea that there is something in between the particles of a gas.
Homework ideas ◆ ◆
Students could write up some of the explanations from Activity 9.3. Coursebook questions 9.11 to 9.13
Topic 4
Gases and the kinetic theory
Coursebook section 9.4 Teaching ideas ◆
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As an introduction to thinking about gases, students need to understand the concepts of pressure and temperature and how these relate to the kinetic model. You can ask your students to act as particles and show various effects: higher temperature means faster; pressure arises from collisions with walls; compressing a gas means more frequent collisions, and so on. Students could answer Coursebook questions 9.14 to 9.16 in pairs and present their answers to the class. Then they could write improved answers having heard a number of attempts. Now you can go on to consider Boyle’s law. Demonstrate this with whatever apparatus you have. Alternatively, Worksheet 9.1 gives some suitable data (and there is more in Table 9.5 of the Coursebook). To analyse the data, students can calculate pressure × volume, and they can plot pressure against volume. Explain how to read the sketch graphs relating pressure and volume (Figure 9.13 in the Coursebook). Worked example 9.1 shows how to use the equation p1V1 = p2V2. Coursebook questions 9.17 to 9.20 can be used to check that your students have grasped these ideas, as can Workbook exercises 9.3 and 9.4. Original material © Cambridge University Press 2014
© Cambridge University Press 2014 IGCSE Physics
Chapter 9: Teaching ideas
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