CHARACTERISTICS OF SOUND
Why is a sound loud, soft, shrill, grave, pleasant or unpleasant? The answer lies in three important characteristics of sound.
Amplitude • Frequency • Wave Form
🎧 Listen & Learn
Sound becomes easier to understand when we connect what we hear with what a vibrating body actually does.
1. The Three Characteristics of Sound
| Characteristic | Depends mainly on | What we experience |
|---|---|---|
| 🔊 Loudness | Amplitude | Sound appears loud or soft |
| 🎵 Pitch | Frequency | Sound appears shrill or grave |
| 🎶 Quality / Timbre | Wave form | Helps us identify the source |
2. Loudness of Sound
Loudness depends mainly on the amplitude of vibration of the vibrating body.
For example, when a drum is struck harder, its membrane vibrates with a greater amplitude and the sound becomes louder.
🔬 Interactive Experiment: Change the Amplitude
Amplitude Simulation
Medium amplitude
3. Pitch of Sound
Pitch depends on the frequency of vibration.
A female voice generally has a higher pitch than a male voice because the frequency of vibration of the vocal cords is generally higher.
Similarly, a baby's cry generally has a higher pitch than the voice of an adult.
🔬 Interactive Experiment: Change the Frequency
Frequency Simulation
Medium pitch
4. Amplitude and Frequency: Do Not Mix Them Up!
| If this increases... | What changes? |
|---|---|
| Amplitude | Loudness increases |
| Frequency | Pitch increases |
| Amplitude decreases | Sound becomes softer |
| Frequency decreases | Sound becomes deeper/graver |
5. Understanding Sound Waves
Consider two waves having the same amplitude but different frequencies. The wave that completes more vibrations in the same time has the greater frequency and therefore the higher pitch.
If the number of waves in the same time interval increases, the frequency increases and the pitch becomes higher.
If the number of waves in the same distance increases, the wavelength decreases and the frequency increases, so the pitch becomes higher.
6. Quality or Timbre
Different sources can produce sounds of the same pitch and loudness, yet we can distinguish them.
For example, a piano and a flute may play the same note, but we can still identify which sound is produced by the piano and which by the flute.
This happens because their wave forms are different.
7. Monotone
A sound having a single frequency is called a monotone.
A tuning fork is a familiar source that produces a sound of a single frequency.
When struck with a suitable rubber pad, its prongs vibrate and produce a nearly pure tone.
8. Tuning Fork: A Special Example
A tuning fork is a U-shaped metallic piece with two arms called prongs and a stem or handle.
When a prong is struck with a rubber pad, the tuning fork vibrates and produces sound.
Different tuning forks can have different frequencies.
9. How Musical Instruments Change Pitch
🎸 Stringed Instruments
In instruments such as the guitar, violin and piano, pitch depends on the vibration of strings.
If a string is stretched more tightly, its frequency of vibration increases and the pitch becomes higher.
🎷 Wind Instruments
In instruments such as the flute, clarinet and shehnai, the vibrating air column is important.
Closing holes in a wind instrument can increase the effective length of the vibrating air column and produce a lower note.
🥁 Membrane Instruments
In instruments such as drums and tablas, a stretched membrane vibrates to produce sound.
10. Bottle and Test-Tube Experiment
Take test tubes or bottles containing different amounts of water. Blow gently across their openings.
When the amount of water is increased, the length of the air column above the water decreases. The sound becomes more shrill.
Therefore: Decreasing length of air column → increasing pitch.
11. A String Experiment
Take a stretched string fixed at both ends. When the string is plucked, it vibrates and produces sound.
If the vibrating length is reduced, the frequency increases and the sound becomes higher in pitch.
12. Quality: Why Can We Recognise a Person by Voice?
Suppose two people speak the same word at approximately the same pitch and loudness. We can still recognise who is speaking.
This is because the wave forms produced by their voices are different. The characteristic wave form gives the sound its quality or timbre.
13. Loudness, Pitch and Quality — One Simple Story
Imagine a school assembly. The microphone produces a sound that is very loud. A student sings a very high note. Then the teacher speaks. All three sounds can be different in:
- Loudness — how strong or soft the sound appears.
- Pitch — whether the sound is high/shrill or low/grave.
- Quality — the character that helps us identify the source.
So when you hear a sound, ask three questions: How loud? How high or low? Who or what produced it?
14. Quick Comparison
| Characteristic | Physical factor | High value gives | Example |
|---|---|---|---|
| Loudness | Amplitude | Louder sound | Harder drum beat |
| Pitch | Frequency | Shriller sound | High musical note |
| Quality | Wave form | Different tone character | Piano vs flute |
15. Think Like a Scientist
Situation 1: A drum is struck harder.
What changes?
Answer: Amplitude increases, so loudness increases.
Situation 2: A guitar string is tightened.
What changes?
Answer: Frequency increases, so pitch increases.
Situation 3: A flute and piano play the same note.
Why can we identify them?
Answer: Their wave forms are different, producing different quality or timbre.
16. Numerical Practice
Q1. A sound source makes 200 vibrations in 2 seconds. Find its frequency.
Solution:
f = 200 ÷ 2 = 100 Hz
Answer: 100 Hz
Q2. A source has a frequency of 250 Hz. How many vibrations does it make in 2 seconds?
= 250 × 2 = 500
Answer: 500 vibrations
17. Rainbow Revision Method 🌈
READ: Read the question carefully.
IDENTIFY: Decide whether it asks about amplitude, frequency or wave form.
UNDERSTAND: Connect the characteristic with what you hear.
CONNECT: Link it with an instrument or daily-life example.
MAP: Make a quick mental map.
APPLY: Use the correct relationship.
EXPLAIN: Explain your answer scientifically.
18. 25 MCQs — Challenge Yourself
🎯 Your Quiz Challenge
Answer the MCQs and check your understanding.
19. Exam Smart Revision
Remember these three golden connections:
PITCH → FREQUENCY
QUALITY / TIMBRE → WAVE FORM
20. Final Challenge
A student says:
“Because Sound A is louder than Sound B, Sound A must also have a higher pitch.”
Is the student correct?
No.
A louder sound has greater amplitude, whereas a higher-pitched sound has greater frequency. The two characteristics are different.
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