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

# 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.