Common misunderstandings and misconceptions ◆
Some students identify the full wave height as the amplitude. It is difficult for them to deduce the frequency from an oscilloscope trace, and this is best left to a higher level.
Homework ideas ◆ ◆
Coursebook questions 12.6 to 12.11 Students could start on Workbook exercise 12.2 Sound as a wave
Topic 4
How sounds travel
Coursebook section 12.4 Teaching ideas ◆
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To understand how sounds travel, students need to have a picture of the particle nature of matter. You could show a stretched spring and discuss how vibrations travel along it – one segment pushes the next, which pushes the next, and so on. It will not be obvious to students why we call this a wave, but you can revisit these ideas later in Chapter 14. Describe how particles push against each other, and how the vibration thus travels through the material. Introduce the terms compression and rarefaction if this is appropriate. Coursebook questions 12.12 to 12.14 sum this up.
Common misunderstandings and misconceptions ◆
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Students may imagine that sound is something other than the motion of particles – that there is some other ‘stuff ’ travelling through (energy, perhaps). Of course, energy is being transferred by the sound, but there are only the particles of the medium and the forces between them. We should acknowledge that the standard diagram of a sound wave (Figure 12.11 in the Coursebook) is perhaps deceptive. The particles of air do not simply oscillate from side to side. They are rushing around at high speeds and this pattern is superimposed on their random motion. They can only change direction when they collide with another molecule.
Homework ideas ◆ ◆ ◆
Coursebook questions 12.12 to 12.14 End-of-chapter questions 1 to 11 Workbook exercise 12.2 Sound as a wave
Original material © Cambridge University Press 2014 © Cambridge University Press 2014 IGCSE Physics
Chapter 12: Teaching ideas
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