G10-7-1 Wave and Sound PDF

# Chapter 7: Wave and Sound When we think of the word waves, water waves on the water surface of a pond and sea waves usually come to mind. Besides these waves there are other types of waves such as sound waves, radio waves, etc. Wave is a basic concept of physics. Energy and momentum are transferr...

# Chapter 7: Wave and Sound When we think of the word waves, water waves on the water surface of a pond and sea waves usually come to mind. Besides these waves there are other types of waves such as sound waves, radio waves, etc. Wave is a basic concept of physics. Energy and momentum are transferred through the medium from the wave source. All waves are produced by a vibrating source. ## Learning Outcomes - Examine wave motion as a form of energy transfer. - Compare transverse and longitudinal waves and give suitable examples of each. - Illustrate displacement-time graph and displacement-position graph. - Express the concept of a wave equation and use it to solve problems. - Describe the reflection, refraction and diffraction of waves. - Apply the basic knowledge of generation, propagation and hearing of sound in daily life. ## 7.1 Describing Wave Motion Wave motion is a method of transferring energy by successive disturbances through the medium. This movement of energy takes place without transferring matter. - Waves are produced if you drop a stone onto a quiet surface of a pond. The waves spread out from the point of impact, carrying energy to all parts of the pond. But the water in the pond does not move from the centre to the edges. This shows that waves transfer energy without transferring matter. - Waves can be produced along a rope by fixed end and moving the other end up and down rapidly. It can be seen that the rope waves move toward the fixed end, while the rope segments only vibrate up and down about their rest (equilibrium) position. The energy from hand is transferred by the rope waves toward the fixed end. The rope is the medium through which the waves move. There are two types of waves: - **Mechanical waves** need a material medium to propagate and cannot pass through a vacuum. Sound waves and seismic waves, which are produced by an earthquake, are mechanical waves. - **Electromagnetic waves** can pass through a vacuum and they do not need a medium for propagation. Light waves and X-rays are electromagnetic waves. ## 7.2 Transverse and Longitudinal Waves Waves are classified as transverse and longitudinal waves depending on the vibration of particles in the medium through which they propagate. - If the displacements of particles of the medium are perpendicular to the direction of the wave, such a wave is called a **transverse wave**. Waves in a vibrating string are transverse waves. They can be demonstrated by moving up and down the free end of a rope (or) slinky spring which is fitted at one end as shown in Figure 7.3. Light waves and other electromagnetic waves are also transverse waves. - If the displacements of particles of medium are parallel to the direction of the waves, such a wave is called a **longitudinal wave**. Compressional waves in a slinky coiled spring and sound waves are longitudinal waves. A longitudinal wave is demonstrated by rapidly pushing forth and pulling back at one end of a slinky coiled spring while another end is fixed. It can be seen that the back and forth movement of the coil is parallel to the wave direction as shown in Figure 7.4. Some waves in nature exhibit a combination of transverse and longitudinal waves. Water waves are a good example of combinational waves. The longitudinal slinky spring wave is represented by a graph (Figure 7.5) which shows the compression and extension of spring segments. This graph is similar to the wave produced by the vibrating rope shown in Figure 7.2.