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Year 10 Science — Sound waves

Say why sound needs a medium, use v = λν and ν = 1/T, work out an echo distance, and place a frequency in the infrasonic, audible or ultrasonic band.

Name: ________________________

Before you start

Two sound waves, drawn one above the other.

12
  1. 1. The quieter wave — a small change in density, so less energy
  2. 2. The louder wave — a large change in density, so more energy

The two waves rise and fall the same number of times across the page, so they share a wavelength and a frequency. What differs is how far the density swings from its average — the amplitude.

  1. 1.A wave has a time period of 0.02 s. What is its frequency, in Hz? Answer with a number.

  2. 2.Put the vacuum bell jar demonstration in order, starting from The bell is rung inside the jar and heard clearly.

    • Air is let back in and the sound returns to its old loudness
    • The bell is rung inside the jar and heard clearly
    • At near vacuum the bell can be seen ringing but barely heard
    • Air is pumped out and the sound grows fainter

  3. 3.A sound wave has a wavelength of 0.5 m and a frequency of 600 Hz. What is its speed, in m/s? Answer with a number.

  4. 4.A tuning fork is struck across the room. What reaches your ear?

    • a) The air particles that were next to the fork
    • b) Energy carried by the sound wave
    • c) Small pieces of the fork itself
    • d) A stream of compressed air from the fork

  5. 5.Sort each description by the band of frequency it belongs to.

    Groups: Infrasonic · Audible to humans · Ultrasonic

    • Between 20 hertz and 20 kilohertz
    • Above 20 kilohertz
    • Waves used to detect earthquakes and volcanic eruptions
    • Waves used to image internal organs without surgery
    • Below 20 hertz
    • Bursts a bat sends out to find its prey

  6. 6.You clap and hear the echo 0.6 s later. Taking the speed of sound as 340 m/s, how far away is the reflecting wall, in m? Answer with a number.

  7. 7.In a large hall a sound seems to hang in the air after the speaker has stopped. What is that called, and what causes it?

    • a) Resonance, from the hall matching the speaker's frequency
    • b) Reverberation, from repeated reflections arriving less than 0.05 s apart
    • c) An echo, from a single reflection arriving more than 0.1 s later
    • d) Refraction, from the sound bending round the pillars

  8. 8.A metal plate is struck harder than before. What changes in the sound wave it sends out?

    • a) Its speed is greater, so it carries more energy
    • b) Its time period is longer, so it carries more energy
    • c) Its wavelength is larger, so it carries more energy
    • d) Its amplitude is larger, so it carries more energy

Answer key — Year 10 Science — Sound waves

  1. 1. 50
  2. 2. 1. The bell is rung inside the jar and heard clearly 2. Air is pumped out and the sound grows fainter 3. At near vacuum the bell can be seen ringing but barely heard 4. Air is let back in and the sound returns to its old loudness
  3. 3. 300
  4. 4. b) Energy carried by the sound wave
  5. 5. Below 20 hertz → Infrasonic; Waves used to detect earthquakes and volcanic eruptions → Infrasonic; Between 20 hertz and 20 kilohertz → Audible to humans; Above 20 kilohertz → Ultrasonic; Waves used to image internal organs without surgery → Ultrasonic; Bursts a bat sends out to find its prey → Ultrasonic
  6. 6. 102
  7. 7. b) Reverberation, from repeated reflections arriving less than 0.05 s apart
  8. 8. d) Its amplitude is larger, so it carries more energy