The document discusses the properties of sound waves. It explains that sound can be reflected, refracted, diffracted, and cause interference effects. This indicates that sound is a wave, as these properties are only exhibited by waves. The document provides examples of constructive and destructive interference of sound waves. It also discusses how the width of an opening affects the diffraction of sound waves passing through it.

1. OBJECTIVES OF LESSON To know that sound can be reflected, refracted, diffracted, and produces interference effects. Know that sound is a wave because it can be reflected and refracted as with particles, diffraction and interference only occur with waves SOUND WAVES

4. In the d iffraction diagram above- the straight parallel waves could be seen to be spreading-out when they go through a gap.

5. What is Wave Interference? Consider two pulses of the same amplitude travelling in different directions along the same medium as shown. Note: During interference snapshots of the medium for two such pulses both waves have an upward displacement. Therefore, there is an upward displacement in the medium which tends to be greater than the displacement of the two interfering pulses as shown in the second diagram. Your task: Draw 2 waves pulses showing destructive interference. Constructive Interference

6. The speed of waves usually changes when they cross a boundary that is the boundary between glass-air, air-glass or water-glass or shallow-deep

7. Questions you may have include: Can the width of the gap affect diffraction of waves? The extent of the spreading depends on how the width of the gap compares to the wavelength of the waves . The bigger the gap width compared with the wavelength of the wave, the less the diffraction . Compare the width of the gaps shown in diagrams A and B. Look at the waves as they go through them.

8. Common examples of diffraction Your task is to suggest other examples to complete the table above (4 minutes Task in pairs of group) Light spreading out through a window Waves spreading through a narrow gap High sound - a short wavelength compared with the gap - little spread. Light spreading out from a torch using the door key hole. Try this easy experiment on your own. Waves spreading into a harbour; narrower gap, wider spread Sound spread-out as you open the door of a room with loud music or sound. In light Waves In water Waves In sound Waves

9. Questions you may have include: What is sound? What are the characteristics of sound? How is sound created and detected?

10. What is Sound? Explain why we think sound is a wave. SOUND WAVES In the study of physics, sound is defined as a range of compression-wave frequencies to which the human ear is sensitive .

11. Ripple tank demonstrations Demonstrate reflection , diffraction , interference , and refraction of water waves.

13. Sound waves are detected when they cause a detector to vibrate. A very common detector to use is a balloon filled with Carbon dioxide placed directly in front of a loudspeaker. Our Eardrum also vibrates from sound waves . This another way to sense sound waves.