Sound
Focused last-minute revision notes with clear concepts, exam traps, key comparisons and compact practice.
Chapter Snapshot
- Sound is produced by vibrating objects.
- Sound needs a material medium and cannot travel through vacuum.
- In humans, sound is produced by vibrating vocal cords in the larynx.
- The eardrum vibrates when sound waves reach the ear.
- Amplitude is related to loudness.
- Frequency is the number of oscillations per second and is measured in hertz (Hz).
- Higher frequency generally means higher pitch.
- The time for one oscillation is the time period.
- Humans typically hear frequencies roughly from 20 Hz to 20,000 Hz.
- Unwanted excessive sound is noise and can damage hearing and health.
What You Will Learn
- Explain sound production by vibration
- Explain why sound needs a medium
- Describe human voice production and hearing
- Define amplitude, time period and frequency
- Relate amplitude to loudness and frequency to pitch
- Use basic frequency/time-period formulas safely
- Explain noise pollution and prevention
Last-Minute Chapter Map
Sound begins with vibration, travels through a medium and is detected when the ear responds to the disturbance.
1. Sound and Vibrations
Sound is produced when an object vibrates, moving repeatedly to and fro about a mean position. A tuning fork, guitar string, drum membrane and speaker cone all produce sound by vibration.
2. Sound Needs a Medium
Sound travels through solids, liquids and gases because particles pass the disturbance from one region to the next. Sound cannot travel through a perfect vacuum because there are no particles to transmit the disturbance.
3. Human Voice
The larynx or voice box contains vocal cords. Air from the lungs passes through the gap between the cords, causing them to vibrate and produce sound. Changes in cord length and tension alter the sound.
4. Human Ear
The outer ear collects sound. Sound reaches the eardrum, causing it to vibrate. These vibrations are transmitted through the middle and inner ear and finally converted into nerve signals sent to the brain.
5. Amplitude, Frequency and Time Period
Amplitude is the maximum displacement from the mean position and is related to loudness. Frequency is the number of oscillations each second and is measured in hertz. Time period is the time for one oscillation. High frequency produces high pitch.
6. Audible Range
A healthy young human typically hears roughly 20 Hz to 20,000 Hz. Frequencies below are infrasonic and above are ultrasonic. Hearing sensitivity varies with age and health.
7. Noise Pollution
Noise from traffic, machinery, loudspeakers and fireworks can disturb sleep, concentration and hearing. Control includes lower volume, silencers, maintenance, sound barriers, green belts and avoiding unnecessary honking.
Loudness vs Pitch
| Feature | Loudness | Pitch |
|---|---|---|
| Main physical link | Amplitude | Frequency |
| Perception | Soft or loud | Low or high tone |
| Example | Gentle vs hard drum strike | Low vs high musical note |
Essential Formula
Frequency and Time Period
f = frequency, N = number of oscillations, t = time, T = time period
Exam Focus
Must Revise Before the Exam
- Vibration
- Need for medium
- Larynx/vocal cords
- Eardrum
- Amplitude and loudness
- Frequency and pitch
- Time period
- Audible range
- Noise pollution
Common Mistakes
Key Terms
Key Terms
Quick Revision
Quick Revision
- Vibrating objects produce sound.
- Sound needs a material medium.
- Vocal cords vibrate in the larynx.
- Eardrum vibrates when sound reaches it.
- Amplitude ↔ loudness.
- Frequency ↔ pitch.
- Frequency unit = hertz (Hz).
- Human hearing ≈ 20–20,000 Hz.
- Noise pollution can harm health and hearing.
Practice Questions
Sound is produced by:
A. vibration
B. only heating
C. magnetism only
D. gravity only
View Solution
Correct Answer: A. vibration
Vibrating objects set the surrounding medium into vibration.
The unit of frequency is:
A. newton
B. pascal
C. hertz
D. joule
View Solution
Correct Answer: C. hertz
Frequency is measured in hertz (Hz).
Pitch mainly depends on:
A. amplitude
B. frequency
C. distance only
D. colour
View Solution
Correct Answer: B. frequency
Higher frequency generally produces higher pitch.
Sound cannot travel through:
A. air
B. water
C. steel
D. vacuum
View Solution
Correct Answer: D. vacuum
Sound requires particles of a material medium.
Differentiate loudness and pitch.
View Solution
Loudness is mainly related to amplitude; pitch is mainly related to frequency.
Why can astronauts not talk to one another directly through empty space without radios?
View Solution
Space is nearly a vacuum and sound cannot travel without a material medium. Radios use electromagnetic waves instead.
A vibrating object completes 50 oscillations in 10 s. Find frequency.
View Solution
Using f = N/t, frequency = 50/10 = 5 Hz.
Chapter Summary
Chapter Summary
- Vibrating objects produce sound.
- Sound needs a material medium.
- Vocal cords vibrate in the larynx.
- Eardrum vibrates when sound reaches it.
- Amplitude ↔ loudness.
- Frequency ↔ pitch.
- Frequency unit = hertz (Hz).
- Human hearing ≈ 20–20,000 Hz.
- Noise pollution can harm health and hearing.