Defects of hearing (A-level only) — AQA A-Level Physics

This topic explores the physics of hearing and the defects that can impair it. You will study the structure of the human ear, including the outer, middle, and inner ear, and how sound waves are transmitted and transduced into electrical signals in the cochlea. Understanding these mechanisms is essential for explaining conductive and sensorineural hearing loss.

Defects of hearing are a key application of wave physics and are relevant to real-world technologies such as hearing aids and cochlear implants. This topic also connects to the broader AQA A-Level Physics specification, particularly waves, resonance, and electrical circuits, and helps develop an appreciation of how physics informs medical treatments.

• →The ear consists of three main regions: outer ear (pinna, ear canal, eardrum), middle ear (ossicles: malleus, incus, stapes), and inner ear (cochlea, auditory nerve).
• →Conductive hearing loss is caused by damage or blockage in the outer or middle ear, reducing the transmission of sound to the cochlea.
• →Sensorineural hearing loss results from damage to hair cells in the cochlea or the auditory nerve, impairing the conversion of sound waves into nerve impulses.
• →Hearing aids amplify sound waves to compensate for conductive loss, while cochlear implants bypass damaged hair cells by electrically stimulating the auditory nerve.
• →The threshold of hearing and the decibel scale are used to quantify hearing loss, with 0 dB being the normal threshold at 1000 Hz.

• Describes equal loudness curves as showing combinations of frequency and intensity that are perceived as equally loud.
• Explains that the threshold of hearing is the lowest equal loudness curve and is frequency dependent.
• States that hearing loss raises the threshold curve, making quieter sounds inaudible.
• Explains that the equal loudness curves become flatter or closer together, indicating a reduced dynamic range.
• Distinguishes noise-induced loss, often with a high-frequency dip, from age-related deterioration, which mainly affects high frequencies.
• Relates the changes to practical consequences such as difficulty hearing speech or increased discomfort at high intensities.

• 💡Sketch or interpret the equal loudness curves with frequency on a logarithmic axis and intensity level on the vertical axis.
• 💡Use the threshold curve to explain why some quiet high-frequency sounds become inaudible first.
• 💡Compare a normal set of curves with a hearing-loss set by describing both the upward shift and the reduced spacing.
• 💡Refer to the dynamic range between threshold and discomfort when explaining everyday listening difficulties.
• 💡Always use precise terminology: 'conductive' vs 'sensorineural', 'transmission' vs 'transduction', and name specific structures like 'ossicles' and 'cochlea'.
• 💡When describing technologies, link each component to its function and the energy conversion involved. For example, microphone: sound to electrical; amplifier: increases electrical signal amplitude.
• 💡For calculation questions on decibels, show the formula and substitution clearly. Remember that hearing loss is the difference in dB between the normal threshold and the impaired threshold.

• Assuming equal loudness curves are horizontal; they are strongly frequency dependent, especially near the threshold.
• Confusing loudness with intensity; equal loudness curves compare perceived loudness, not equal intensity.
• Stating that hearing loss only shifts the threshold without changing the spacing of the curves; the curves also flatten as dynamic range is reduced.
• Describing physiological mechanisms such as hair cell damage when the question excludes physiological changes; focus on the perceptual and curve-based effects.
• Students often think that hearing aids can cure all types of hearing loss. In fact, they are most effective for conductive loss and mild to moderate sensorineural loss; severe sensorineural loss may require a cochlear implant.
• Many believe that sensorineural hearing loss is always caused by loud noises. While noise-induced damage is common, it can also result from ageing, infections, or genetic factors.
• Some confuse the role of the ossicles with that of the cochlea. The ossicles amplify and transmit vibrations to the cochlea, but the cochlea is where transduction into electrical signals occurs.

1. 1Day 1-2: Learn the structure and function of the ear. Create a labelled diagram and annotate each part with its role in hearing.
2. 2Day 3-4: Study conductive and sensorineural hearing loss. Make a table comparing causes, affected structures, and symptoms.
3. 3Day 5-6: Investigate hearing aids and cochlear implants. Draw flowcharts showing the path of sound and electrical signals.
4. 4Day 7-8: Practice calculations on sound intensity level and hearing loss. Use past paper questions to test your understanding.
5. 5Day 9-10: Review common exam questions and mark schemes. Focus on 6-mark explanations and ensure you can write concise, accurate answers.

• 📋Definition and explanation questions: e.g., 'Describe the difference between conductive and sensorineural hearing loss.' Advice: Use clear definitions and give specific causes for each.
• 📋Calculation questions: e.g., 'Calculate the hearing loss in dB given threshold intensities.' Advice: Write the formula, substitute values, and show working.
• 📋Explanation of technology: e.g., 'Explain how a cochlear implant works.' Advice: Describe the components and the energy conversions, and state that it bypasses damaged hair cells.
• 📋Data analysis: e.g., 'Interpret an audiogram to identify the type of hearing loss.' Advice: Look for patterns: conductive loss affects all frequencies similarly, while sensorineural loss often affects high frequencies more.