CORE Physics (Short Course) - 9223 OxfordAQA

Sound And Ultrasound

Muhtasari

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.

Malengo

  1. 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.
  2. 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.
  3. Sound waves can be reflected (echoes) and diffracted.

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Maelezo ya Somo

A loudspeaker cone pushes forward and the air just in front of it has nowhere to go, so it becomes momentarily crowded. The cone pulls back and that same patch of air is left thinned out. Repeat that a few hundred times a second and a train of crowded and thinned regions sets off across the room at about 340 metres per second. Nothing has been sent anywhere: the same air molecules are still in front of the speaker, jiggling to and fro over a distance far smaller than the width of a hair. What travelled was the pattern, and the energy carried in it.

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Tathmini ya Somo

Hongera kwa kukamilisha somo la Sound And Ultrasound. Sasa kwa kuwa umechunguza dhana na mawazo muhimu, ni wakati wa kuweka ujuzi wako kwa mtihani. Sehemu hii inatoa mazoezi mbalimbali maswali yaliyoundwa ili kuimarisha uelewaji wako na kukusaidia kupima ufahamu wako wa nyenzo.

Utakutana na mchanganyiko wa aina mbalimbali za maswali, ikiwemo maswali ya kuchagua jibu sahihi, maswali ya majibu mafupi, na maswali ya insha. Kila swali limebuniwa kwa umakini ili kupima vipengele tofauti vya maarifa yako na ujuzi wa kufikiri kwa makini.

Tumia sehemu hii ya tathmini kama fursa ya kuimarisha uelewa wako wa mada na kubaini maeneo yoyote ambapo unaweza kuhitaji kusoma zaidi. Usikatishwe tamaa na changamoto zozote utakazokutana nazo; badala yake, zitazame kama fursa za kukua na kuboresha.

  1. 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
  2. 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
  3. 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
  4. 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
  5. 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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