Optional Unit V: Sound

A. Applications

1. The Human Ear

Key Concepts

Sound waves travel through the meatus (auditory canal) to the tympanic membrane(ear drum). Frequencies between 20 Hz and 20 000 Hz are audible. The auditory canal can resonate and amplify sounds within a frequency range of about 2 000 Hz to 5 500 Hz by up to a factor of 10.

Successive compressions and rarefactions of air reaching the eardrum result in a change in pressure between the outer ear and the middle ear. The Eustachian tube helps to keep the middle ear at atmospheric pressure.

The difference in pressure between the sound wave striking the outer surface of the eardrum and normal atmospheric pressure on the inside of the eardrum causes the eardrum to vibrate.

Within the middle ear, vibrations travel through three small bones (the hammer, anvil, and stirrup) to the cochlea. The bones act as interlocking levers which amplify the force of the eardrum striking the hammer. The oval window of the cochlea is smaller than the eardrum. This causes a further amplification of the sound vibration.

The semicircular canals act as miniature accelerometers. They also help to maintain a sense of balance by responding to gravity and changes in acceleration. The hair-like structures (dendrites) in the cochlea resonate at various different frequencies. The vibrations stimulate neurons to produce electrical impulses which are sent along the auditory nerve to the brain for processing .

Learning Outcomes

Students will increase their abilities to:

1. Define the following terms: meatus (auditory canal), tympanic membrane (eardrum), cochlea, auditory nerve, Eustachian tube.

2. Identify some important physical principles involved in human hearing such as: amplification, levers, accelerometers, resonance, longitudinal waves, and pressure.

3. Explain the physical process by which sound signals reaching the ear are transferred from the outer ear to the middle ear.

Teaching Suggestions, Activities and Demonstrations

1. Research the permissible levels of sound intensity in various workplaces. Find out why these regulations exist, and who is responsible for establishing and maintaining them. Identify protective equipment used to maintain safe noise levels.

2. Label the parts of the ear on a diagram.

3. Develop an awareness and understanding of hearing impairments. If possible, invite a hearing impaired person, or someone who works with the hearing impaired, to explain how people learn to adapt and function successfully in spite of their hearing impairments.