Sound: Properties, Transmission and the Ear

What you'll learn

This revision guide covers the complete CSEC specification on sound, including how sound waves are produced and transmitted, their measurable properties, and the structure and function of the human ear. You'll learn to explain wave behaviour, calculate speed of sound, and describe hearing processes — all critical for Paper 1 multiple choice and Paper 2 structured questions.

Key terms and definitions

Frequency — the number of complete waves (or vibrations) produced per second, measured in hertz (Hz); determines the pitch of a sound

Amplitude — the maximum displacement of particles from their rest position in a sound wave; determines the loudness or intensity of the sound

Longitudinal wave — a wave in which particles vibrate parallel to the direction of energy transfer, producing compressions and rarefactions

Compression — a region in a longitudinal wave where particles are pushed closer together, creating higher pressure

Rarefaction — a region in a longitudinal wave where particles are spread further apart, creating lower pressure

Pitch — how high or low a sound appears to a listener; directly related to the frequency of the sound wave

Echo — a reflected sound wave that returns to the listener after bouncing off a surface

Decibel (dB) — the unit used to measure sound intensity or loudness level

Core concepts

Nature and production of sound

Sound is produced when objects vibrate. These vibrations create disturbances in the surrounding medium (usually air) that travel outward as waves. Common examples in Caribbean contexts include:

• Steel pan vibrations producing different notes in a steelband
• Vocal cord vibrations in calypso singers
• Drumheads vibrating in traditional drumming ensembles
• Engine vibrations from fishing boats

Sound travels as a longitudinal wave. Unlike transverse waves (such as light), the particles in a sound wave vibrate back and forth in the same direction that the wave travels. This creates alternating regions of compression and rarefaction as the wave moves through the medium.

Key characteristics:

• Sound requires a medium to travel (solid, liquid or gas)
• Sound cannot travel through a vacuum
• The particles of the medium do not travel with the wave — only the energy transfers
• Each particle oscillates about its rest position and transfers energy to neighbouring particles

Properties of sound waves

Sound waves have measurable properties that determine what we hear:

Frequency and pitch:

• Frequency is measured in hertz (Hz) or kilohertz (kHz)
• 1 Hz = 1 vibration per second
• High frequency = high pitch (e.g., whistle, soprano voice)
• Low frequency = low pitch (e.g., bass drum, male voice)
• Human hearing range: approximately 20 Hz to 20,000 Hz (20 kHz)
• Sounds above 20 kHz are called ultrasound
• Sounds below 20 Hz are called infrasound

Amplitude and loudness:

• Greater amplitude = louder sound
• Smaller amplitude = quieter sound
• Loudness is measured in decibels (dB)
• Prolonged exposure to sounds above 85 dB can damage hearing
• Caribbean contexts: loud music at carnival events (often exceeding 100 dB), construction noise in developing areas

Wavelength:

• Distance between two consecutive compressions or rarefactions
• Related to frequency by the wave equation: speed = frequency × wavelength
• Shorter wavelength corresponds to higher frequency (higher pitch)
• Longer wavelength corresponds to lower frequency (lower pitch)

Speed of sound in different media

Sound travels at different speeds depending on the medium:

General pattern:

• Fastest in solids
• Slower in liquids
• Slowest in gases

Typical values you should know:

• Air (at 20°C): approximately 340 m/s or 330 m/s (both values accepted at CSEC level)
• Water: approximately 1500 m/s
• Steel: approximately 5000 m/s

Why does speed vary?

In solids, particles are tightly packed and strongly bonded, allowing vibrations to transfer quickly from particle to particle. In gases, particles are far apart and collisions are less frequent, slowing the transfer of vibrations.

Temperature also affects speed in air — warmer air allows faster sound transmission because particles have more kinetic energy and collide more frequently.

Wave equation:

The relationship between speed, frequency and wavelength is:

speed = frequency × wavelength

or: v = f × λ

where v = speed (m/s), f = frequency (Hz), λ = wavelength (m)

Reflection of sound and echoes

Sound waves obey the law of reflection, just like light:

angle of incidence = angle of reflection

When sound reflects off a hard surface (wall, cliff, building), it produces an echo. For humans to distinguish an echo from the original sound, the reflecting surface must be at least 17 metres away. This is because the sound must take at least 0.1 seconds to travel to the surface and back for our ears to perceive them as separate sounds.

Calculation for echoes:

If a sound reflects off a surface and returns, the total distance travelled is twice the distance to the surface:

total distance = 2 × distance to reflector

Using: speed = distance ÷ time

Caribbean applications:

• Sonar technology used by fishing vessels to locate fish schools
• Echo-sounding to measure sea depth in Caribbean waters
• Ultrasound imaging in regional hospitals

Structure and function of the human ear

The ear converts sound waves into electrical signals that the brain interprets. It has three main sections:

Outer ear:

• Pinna (auricle) — the visible external flap of cartilage that collects and funnels sound waves
• Ear canal (auditory canal) — a tube approximately 2.5 cm long that channels sound toward the eardrum
• Produces wax to trap dust and foreign particles

Middle ear:

• Eardrum (tympanic membrane) — a thin membrane that vibrates when sound waves strike it
• Three tiny bones called ossicles (the smallest bones in the body):
  • Hammer (malleus) — attached to the eardrum
  • Anvil (incus) — middle bone
  • Stirrup (stapes) — connects to the oval window
• The ossicles amplify the vibrations and transmit them to the inner ear
• Connected to the throat by the Eustachian tube, which equalizes air pressure on both sides of the eardrum

Inner ear:

• Oval window — membrane that receives vibrations from the stirrup
• Cochlea — a spiral, fluid-filled tube containing thousands of tiny hair cells (sensory receptors)
• Vibrations in the cochlear fluid cause hair cells to bend, generating electrical impulses
• Auditory nerve — carries electrical signals to the brain for interpretation
• Semicircular canals — involved in balance (not directly in hearing)

How we hear: the pathway

1. Sound waves are collected by the pinna
2. Waves travel down the ear canal to the eardrum
3. Eardrum vibrates at the same frequency as the sound wave
4. Vibrations pass through the three ossicles (hammer → anvil → stirrup)
5. Ossicles amplify the vibrations
6. Stirrup pushes on the oval window
7. Pressure waves travel through fluid in the cochlea
8. Hair cells in the cochlea bend and produce electrical impulses
9. Auditory nerve transmits impulses to the brain
10. Brain interprets the signals as sound

Hearing problems and protection

Common causes of hearing damage:

• Prolonged exposure to loud sounds (above 85 dB)
• Sudden very loud noises (explosions, gunshots)
• Ear infections damaging the eardrum or ossicles
• Age-related deterioration of hair cells in the cochlea
• Blockage of the ear canal with wax

Protecting your hearing:

• Use ear protection in noisy environments (construction sites, airports, loud factories)
• Keep personal music device volume below maximum
• Take breaks from loud environments
• Treat ear infections promptly
• Regular hearing checks, especially for workers in noisy industries (e.g., Caribbean steel mills, port operations)

Deafness types:

• Conduction deafness — problem in outer or middle ear prevents sound transmission (e.g., damaged eardrum, fused ossicles); can often be corrected with hearing aids or surgery
• Nerve deafness — damage to cochlea or auditory nerve; often permanent as hair cells cannot regenerate

Worked examples

Example 1: Calculating speed of sound

Question: A student stands 85 metres from a large wall and claps once. She hears the echo 0.5 seconds later. Calculate the speed of sound in air. [3 marks]

Solution:

Step 1: Identify what you know

• Distance to wall = 85 m
• Time taken = 0.5 s
• Sound travels to the wall AND back

Step 2: Calculate total distance travelled Total distance = 2 × 85 m = 170 m [1 mark]

Step 3: Use the equation speed = distance ÷ time Speed = 170 m ÷ 0.5 s [1 mark] Speed = 340 m/s [1 mark]

Mark scheme notes: Students must remember to double the distance. A common error is using only 85 m, giving 170 m/s — this scores only 1 mark for method.

Example 2: Wave equation problem

Question: A steel pan produces a musical note with a frequency of 680 Hz. If the speed of sound in air is 340 m/s, calculate the wavelength of this sound. [3 marks]

Solution:

Step 1: Write down the wave equation speed = frequency × wavelength [1 mark] or v = f × λ

Step 2: Rearrange for wavelength wavelength = speed ÷ frequency [1 mark]

Step 3: Substitute values and calculate λ = 340 m/s ÷ 680 Hz λ = 0.5 m [1 mark]

Alternative acceptable answer: 50 cm

Example 3: Ear structure and function

Question: (a) Name the three small bones in the middle ear. [3 marks] (b) State the function of these bones. [2 marks] (c) Explain why the cochlea is important for hearing. [3 marks]

Solution:

(a) Hammer (malleus), anvil (incus), and stirrup (stapes) [3 marks — 1 mark each; accept scientific names in brackets]

(b) The three bones amplify vibrations from the eardrum [1 mark] and transmit them to the oval window/inner ear [1 mark]

(c) The cochlea contains fluid [1 mark] and tiny hair cells [1 mark]. When the fluid vibrates, hair cells bend and produce electrical impulses/nerve signals that travel to the brain [1 mark]. [Award marks for any three valid points about cochlea function]

Common mistakes and how to avoid them

• Forgetting to double the distance in echo calculations. Remember: sound travels TO the reflector AND back, so total distance = 2 × distance to object. Always write this step clearly.

• Confusing frequency with amplitude. Frequency determines pitch (how high or low); amplitude determines loudness (how loud or soft). High frequency ≠ loud sound.

• Saying "sound travels faster in air than in water." This is backwards. Sound travels faster in liquids and solids than in gases. The correct order is: solids > liquids > gases.

• Mixing up the order of ear structures. Learn the pathway: pinna → ear canal → eardrum → ossicles → oval window → cochlea → auditory nerve → brain. Questions often test the sequence.

• Stating that sound can travel through a vacuum. Sound requires particles to transmit vibrations, so it cannot travel through space/vacuum. Light can travel through a vacuum, but sound cannot.

• Forgetting units in calculations. Always include units: speed in m/s, frequency in Hz, wavelength in m, time in s. Marks are often deducted for missing units even when the number is correct.

Exam technique for "Sound: Properties, Transmission and the Ear"

• For "state" questions (1-2 marks): Give a brief, factual answer without explanation. Example: "State one property of sound waves" requires only "longitudinal wave" or "requires a medium" — no need to explain why.

• For "explain" questions (3-4 marks): Show cause and effect. Use linking words like "because," "therefore," "this causes," "as a result." Example: "Explain why sound travels faster in water than in air" — mention particle arrangement AND how this affects vibration transfer.

• Calculations always show working. Even if you make an arithmetic error, you can still earn method marks if your approach is correct. Write the formula first, then substitute, then calculate.

• Labelling diagrams of the ear: Learn the exact names. "Ear bone" won't earn the mark instead of "hammer" or "ossicle." The examiner follows a strict mark scheme with specific terminology.

Quick revision summary

Sound is a longitudinal wave produced by vibrations, requiring a medium to travel. It travels fastest in solids, slower in liquids, and slowest in gases. Frequency determines pitch; amplitude determines loudness. Human hearing ranges from 20 Hz to 20 kHz. The ear has three sections: outer (pinna, ear canal), middle (eardrum, three ossicles), and inner (cochlea with hair cells). Sound waves cause the eardrum to vibrate; ossicles amplify these vibrations; cochlear hair cells convert them to electrical signals sent via the auditory nerve to the brain.