Home » Handbook of O Level Physics » UNIT 16: SOUND


  • Sound: It is a longitudinal wave that

    • emanates from a vibrating source

    • and requires a material medium

  • Speed of sound

    • In air: About 330 m/s

    • In liquids: About 5 times faster (than in air)

    • In solids: About 15 times faster (than in air)

  • Audibility

    • The human ear can detect sounds having a frequency between 20 Hz and 20 kHz.

    • The human ear cannot detect infra-sounds (below 20 Hz) and ultra-sounds (above 20 kHz).

  • Applications of sound and ultrasound

    • Ultrasonic cleaning of machine parts

    • Medical examination of the body

    • Echoes are used to find depth or to detect mines or shoals of fish

  • Echo: It is the reflection of sound.

  • Reverberation is the effect in which you hear a prolonged sound because different echoes are reaching your ears one after the other (like in a large hall).

  • Characteristics of sound

    • Loudness

      • It depends upon amplitude. Sounds can be soft or loud.

    • Pitch

      • It depends upon frequency. Sounds can be low or high.

    • Quality (or timbre)

      • Different audio-instruments playing the same note (same loudness and pitch) sound different.

      • This is because these instruments superimpose their own additional sounds (harmonics).

      • Therefore the resulting wave-forms from two different audio-instruments are different.

  • Experiments

    • Measuring speed of sound in air

      • Method 1 is to use a stop watch and a pistol.

      • Method 2 is to use an echo from a wall.

      Note: In both methods use the formula: s = d / t

    • Studying reflection of sound

      • Use two pipes next to a wall. Sound heard is loudest when angle of incidence equals angle of reflection.

Go back to table of contents

Have questions? See our compilation of questions and answers.