Sound And Ultrasound
Overview
Hold a finger against your throat and hum. What you feel is the whole of this topic in one sensation: something is shaking, and because it is shaking you can hear it. Every sound that has ever reached you began as a vibration and arrived as a vibration, carried across the room by air that squashes and stretches hundreds of times a second without ever travelling anywhere itself. Take the air away and the vibration has nothing to ride on, which is why the loudest explosion in space would reach you in complete silence.
This lesson takes that idea and turns it into physics you can calculate with. You will learn why a note is high or low, why it is quiet or deafening, and where the two limits of your own hearing sit. Then you will make sound do two things that every wave does: bounce off a hard surface, and spread as it comes through a gap. The first of those turns a clap and a stopwatch into a way of measuring how fast sound travels; the second explains why you can hear a conversation in the next room without being able to see anyone having it.
Objectives
- Sound waves are longitudinal waves and cause vibrations in a medium, which are detected as sound. The range of human hearing is about 20 Hz to 20 000 Hz. No details of the structure of the ear are required.
- The pitch of a sound is determined by the frequency of vibrations of the source. Its loudness is related to the size of the amplitude of the disturbance.
- Sound waves can be reflected (echoes) and diffracted.
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Sound And Ultrasound. Now that you've explored the key concepts and ideas, it's time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- What type of wave is a sound wave? A. A transverse wave B. A longitudinal wave C. An electromagnetic wave D. A wave that needs no medium Answer: B
- What is the approximate range of frequencies that a human can hear? A. 2 Hz to 2000 Hz B. 20 Hz to 20 000 Hz C. 200 Hz to 200 000 Hz D. 20 000 Hz to 2 000 000 Hz Answer: B
- A guitar string is plucked harder but is not shortened or retuned. What happens to the sound? A. It becomes louder and higher in pitch B. It becomes louder with the pitch unchanged C. It becomes higher in pitch with the loudness unchanged D. It becomes quieter and lower in pitch Answer: B
- A student stands 170 m from a vertical cliff, claps once and hears the echo 1.0 s later. What is the speed of sound in air? A. 85 m/s B. 340 m/s C. 170 m/s D. 680 m/s Answer: B
- Why can you hear someone talking in the next room through an open doorway when you cannot see them? A. Sound travels much faster than light B. The wavelength of the sound is comparable to the width of the doorway so it diffracts strongly, while the wavelength of light is far smaller so it barely spreads C. Sound is a transverse wave and light is a longitudinal wave D. Light needs a medium to travel through and sound does not Answer: B
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Recommended Books
Further learning from open sources
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Textbook section
Speed of Sound, Frequency, and Wavelength
Relate the characteristics of waves to properties of sound waves
"Physics: Speed of Sound, Frequency, and Wavelength" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/physics/pages/14-1-speed-of-sound-frequency-and-wavelength. Access for free at https://openstax.org/books/physics/pages/1-introduction
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Textbook section
Sound Intensity and Sound Level
Relate amplitude of a wave to loudness and energy of a sound wave
"Physics: Sound Intensity and Sound Level" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/physics/pages/14-2-sound-intensity-and-sound-level. Access for free at https://openstax.org/books/physics/pages/1-introduction
Published by other organisations under open licences, credited as they ask. Links open their websites.
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