3.4 Sound (3)
Resources |
Revision Questions |
Physics
Login to see all questions
Click on a question to view the answer
1.
A student performs an experiment to investigate echoes. They measure the time it takes for a sound to travel to a wall and back. List three factors that could affect the accuracy of their measurements and explain how each factor would influence the results.
Here are three factors that could affect the accuracy of a student's echo experiment:
- Temperature: The speed of sound in air is affected by temperature. Higher temperatures increase the speed of sound, meaning the time measured will be shorter than the actual time for the sound to travel to and from the wall. This would lead to an underestimation of the actual time.
- Humidity: Humidity can also affect the speed of sound, although the effect is less pronounced than temperature. Higher humidity generally increases the speed of sound slightly. This would have a similar effect to temperature, leading to an underestimation of the actual time.
- Obstructions or Noise: Any obstructions in the path of the sound wave (e.g., objects in the room) or background noise can interfere with the measurement. Obstructions can cause multiple echoes or distort the original sound, making it difficult to accurately determine the time. Noise can mask the echo, making it harder to detect and measure. This would lead to inaccurate time measurements.
2.
Sound waves are a form of energy that travel through a medium. Explain why sound cannot travel through a vacuum. Your answer should include a discussion of the properties of matter and how they relate to sound transmission.
Sound waves are mechanical waves, meaning they require a medium (solid, liquid, or gas) to propagate. This is because sound transmission involves the vibration of particles within the medium. Matter is composed of particles that are held together by forces. These particles can transfer kinetic energy through collisions.
In a vacuum, there are no particles present. Therefore, there is nothing for the sound waves to vibrate or collide with. The energy from the sound wave cannot be transferred from one point to another because there is no medium to carry the disturbance.
Consider the example of sound from a loudspeaker. The speaker cone vibrates, causing the air molecules around it to vibrate. These vibrating air molecules then bump into their neighbours, transferring the vibration outwards. This chain of collisions allows the sound wave to travel. Without air molecules (as in a vacuum), this chain cannot occur.
3.
Question 1
Describe three different uses of ultrasound in the nondestructive testing of materials. For each use, explain the principle of operation and the type of material it is most suitable for.
Ultrasound in nondestructive testing (NDT) uses high-frequency sound waves to detect flaws and imperfections within materials without causing damage. Here are three uses:
- Material Flaw Detection: Ultrasound pulses are transmitted into the material. Reflections from internal flaws (e.g., cracks, voids, inclusions) are detected by a receiver. The time it takes for the ultrasound to travel to the flaw and back is measured. The principle is based on the reflection of sound waves at interfaces. Suitable for metals, plastics, and composites.
- Thickness Measurement: Similar to flaw detection, ultrasound is used to measure the thickness of materials. The time-of-flight of the ultrasound pulse is measured and related to the thickness. This is a non-destructive way to assess material integrity. Suitable for metals, plastics, and composites.
- Coupling and Bonding Inspection: Ultrasound can be used to assess the quality of the coupling between two materials or the strength of a bond. By sending ultrasound through the interface, any air gaps or weak points in the bond can be detected. The principle relies on changes in the acoustic impedance at the interface. Suitable for a variety of materials used in bonding applications.