Sound And Ultrasound
Aperçu
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.
Objectifs
- 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.
Carte mentale
Ce theme est schematise pour montrer comment les idees se relient.
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Note de cours
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Évaluation de la leçon
Félicitations, vous avez terminé la leçon sur Sound And Ultrasound. Maintenant que vous avez exploré le concepts et idées clés, il est temps de mettre vos connaissances à lépreuve. Cette section propose une variété de pratiques des questions conçues pour renforcer votre compréhension et vous aider à évaluer votre compréhension de la matière.
Vous rencontrerez un mélange de types de questions, y compris des questions à choix multiple, des questions à réponse courte et des questions de rédaction. Chaque question est soigneusement conçue pour évaluer différents aspects de vos connaissances et de vos compétences en pensée critique.
Utilisez cette section d'évaluation comme une occasion de renforcer votre compréhension du sujet et d'identifier les domaines où vous pourriez avoir besoin d'étudier davantage. Ne soyez pas découragé par les défis que vous rencontrez ; considérez-les plutôt comme des opportunités de croissance et d'amélioration.
- 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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