Sound waves and the ear

Question 1

vibrations and waves

Answer 1

when objects vibrate sound waves are produced

these sound waves are a series of oscillations that transfer energy from one source to the ear

energy travels via a longitudinal wave

(e.g. vibration of a guitar string to produce a musical note
the length, thickness and material determines the frequency of the note)

Question 2

frequency range of the human ear

Answer 2

typically 20 Hz to 20 kHz

can’t hear below 20 Hz or above 20 kHz

Question 3

how sound waves are produced

Answer 3

after a drum is hit, the vibration of the drum will cause a longitudinal wave to move outwards from it

using the example of a drum:

• the drum skin starts to vibrate and particles of air next to the drum skin are compressed as it moves outwards
• the drum skin springs back and the particles of air next to its surface now move apart again
• the compressed particles continue to move away from the drum, creating a wave

Question 4

how the ear detects sound

Answer 4

sound waves enter through the external ear (pinna)

they are channelled down the ear canal and cause the eardrum to vibrate

threes small bones then transmit vibrations to the cochlea

this produces electrical signals which pass through the auditory nerve to the brain, where they are interpreted as sound

Question 5

Explain why the human ear can only hear sounds in the range 20Hz to 20,000Hz [2]

Answer 5

sound waves travelling from air into a solid are converted to vibrations and travel through the solid as a series of vibrations

this conversion of sound waves to vibrations in solids only works over a limited frequency range, which is from 20Hz to 20kHz, so the eardrum doesn’t vibrate

(the frequency of vibration is the same in sound waves as in the solids it is vibrating
solids can be made to vibrate, but not by every frequency)

Question 6

Explain what the ear does in terms of the energy transfer that takes place in the ear [3]

Answer 6

kinetic energy of the air molecules carrying the sound waves
is transferred into electrical energy
by vibrations inside the ear, and the electrical signal is taken to the brain

Question 7

Explain how a vibration becomes a sound that is heard [3]

Answer 7

an object vibrates/moves backwards and forwards,
pushing the air molecules into a series of compressions and rarefactions
that are transmitted as a pressure wave

(the series of compressions/rarefactions becomes a wave that vibrates air particles, if it reaches an ear it causes the eardrum to vibrate, allowing us to hear it)

Question 8

Explain why sound waves are often described by scientists in terms of their frequencies rather than their wave speed [4]

Answer 8

sound waves have the same frequency as the vibrations that cause them, and this does not change when a sound wave passes from one material into another,
whereas wave speed does, as the wave speed/wavelength is different in different materials