Musical Instruments: String, Wind, Membrane and Monotone (ICSE Class 8 Physics)
Updated 17 October 2026 · Fact-checked
In string instruments a shorter, tighter, thinner string gives a higher pitch; in wind instruments a shorter air column gives a higher pitch; in membrane instruments a tighter or smaller membrane gives a higher pitch. A monotone is a sound of one steady pitch.
Understand Musical Instruments and Monotone
String instruments (sitar, guitar, violin): a stretched string vibrates. The pitch (frequency) is higher when the string is
- shorter (pressing a finger on the string shortens the vibrating part),
- tighter (turning the pegs increases the tension),
- thinner (thin strings give the high notes).
The hollow wooden body makes the sound louder by setting more air in vibration.
Wind instruments (flute, whistle, shehnai): a column of air vibrates.
- A shorter air column gives a higher pitch.
- Covering or uncovering holes of a flute changes the length of the vibrating air column.
- In a bottle jal tarang, blowing across the tops gives a higher pitch for the bottle with more water, because its air column is shorter.
Membrane instruments (tabla, drum, dholak): a stretched skin vibrates when struck.
- A tighter membrane gives a higher pitch (tabla players tap the blocks to tighten or loosen the skin).
- A smaller drum generally gives a higher pitch than a large one.
- Striking harder gives a louder sound (larger amplitude), not a higher pitch.
Monotone. A sound that stays at one single pitch, without rising or falling, is a monotone. A tuning fork gives a steady note of one frequency, and an alarm beep or a dial tone is a monotone. Speech and music are pleasant because the pitch varies; reading aloud at one pitch sounds dull.
Summary table.
| Instrument | What vibrates | Higher pitch if |
|---|---|---|
| String | string | shorter, tighter, thinner |
| Wind | air column | shorter column |
| Membrane | stretched skin | tighter, smaller |
Musical Instruments and Monotone: formulas and key facts
- String instruments
- Higher pitch: shorter
- tighter
- thinner string
- Body makes the sound louder.
- Wind instruments
- Higher pitch: shorter air column | more holes uncovered
- Jal tarang: more water, higher pitch.
- Membrane instruments
- Higher pitch: tighter | smaller membrane
- Harder strike: louder, not higher.
How to solve Musical Instruments and Monotone questions
First name what vibrates, then use the rule for that instrument.
- 1Decide: string, air column or membrane.
- 2Apply the rule: shorter, tighter, thinner or smaller means higher pitch.
- 3For comparisons, change one factor at a time.
- 4Use amplitude for loudness, frequency for pitch.
Musical Instruments and Monotone in real life
Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.
Jal tarang bottles
Suppose three identical bottles, each 25 cm tall, contain water to heights 5 cm, 10 cm and 15 cm, and you blow across their tops.
Find the length of the air column in each and arrange the notes from lowest to highest pitch.
Try it first, then show the solutionSolution
- Air columns: cm, cm, cm.
- A shorter air column gives a higher pitch.
Answer: 20, 15 and 10 cm; the pitch is lowest for the 5 cm of water and highest for the 15 cm.
Memory hook: More water, shorter air, higher note.
Tuning a guitar
Imagine a guitarist turns the peg of one string until it is tighter.
What happens to its pitch?
Try it first, then show the solutionSolution
- A tighter string vibrates faster.
- The frequency increases, so the pitch rises.
Answer: The pitch rises.
Memory hook: Tighter string, higher pitch.
Tricks to remember Musical Instruments and Monotone
Short memory aids. Say each one aloud once, then use it on a question the same day.
Short, tight, thin
High note from a string: short, tight, thin.
Use it when: Strings.
More water, higher
Jal tarang: more water leaves less air, so a higher note.
Use it when: Wind.
Tight skin sings high
Tighten the tabla, raise the note.
Use it when: Membranes.
Musical Instruments and Monotone: solved examples
Ordered from board level to HOTS. Try each one before you open the solution.
Example 1: Which string is higher? · 1 mark · MCQBoard level
The pitch of a string is higher when the string is:
(a) longer
(b) looser
(c) thicker
(d) shorter
Try it first, then show the solutionSolution
- Pressing the string shortens the vibrating length and raises the pitch.
Answer: (d) shorter
Example 2: Tuning a tabla · 2 marks · Short answerBoard level
How does a tabla player raise the pitch of the tabla? Which quantity of the vibration changes, frequency or amplitude?
Try it first, then show the solutionSolution
- By tightening the membrane (tapping the wooden blocks under the straps). (1)
- The frequency increases. (1)
Answer: Tighter membrane; frequency increases.
Example 3: Jal tarang · 3 marks · Short answerHarder board level
Three identical bottles, 25 cm tall, hold water up to 5 cm, 10 cm and 15 cm. Blowing across their tops produces notes. (a) Find the air columns. (b) Which bottle gives the highest note? Explain.
Try it first, then show the solutionSolution
- (a) 20 cm, 15 cm and 10 cm. (1)
- (b) The bottle with 15 cm of water. (1)
- Its air column is the shortest, and a shorter air column vibrates faster, giving a higher pitch. (1)
Answer: (a) 20, 15, 10 cm (b) 15 cm of water
Example 4: Three drums · 3 marks · Short answerHarder board level
Drum A is large and loose, drum B is small and loose, drum C is small and tight. Arrange them in increasing order of pitch and explain. Which factor is shown by comparing B and C?
Try it first, then show the solutionSolution
- A < B < C. (1)
- A larger drum gives a lower pitch than a small one; a tight membrane gives a higher pitch than a loose one. (1)
- B and C show the effect of tightness (size is the same). (1)
Answer: A, B, C; B and C show tightness
Example 5: Which sitar string? · 4 marks · Case-basedHOTS / competency
Three strings are plucked: A is 60 cm long, thin, and at tension T; B is 60 cm long, thick, and at tension T; C is 40 cm long, thin, and at tension T. (a) Arrange A, B and C in order of increasing pitch. (b) Name the factor that distinguishes A from B. (c) Name the factor that distinguishes A from C. (d) What would happen to A's pitch if the peg were turned to increase the tension?
Try it first, then show the solutionSolution
- (a) B < A < C. (1)
- (b) Thickness (thicker, lower). (1)
- (c) Length (shorter, higher). (1)
- (d) The pitch rises. (1)
Answer: (a) B, A, C (b) thickness (c) length (d) rises
Where students lose marks in Musical Instruments and Monotone
The slips examiners see most often, and what to write instead.
Mistake: Reversing the air-column rule
Shorter air column gives higher pitch.
Wrong working
"More water gives a lower note because it is heavier."
Right working
"More water gives a shorter air column, so a higher note."
Do this: Think about the air, not the water.
Mistake: Louder means higher
Hitting harder changes loudness only.
Wrong working
"Strike the drum harder for a higher pitch."
Right working
"Strike harder for a louder sound; tighten for higher pitch."
Do this: Separate amplitude from frequency.
Mistake: Wrong thickness rule
Thin strings give higher notes.
Wrong working
"A thicker string gives a higher pitch."
Right working
"A thinner string gives a higher pitch."
Do this: Short, tight, thin: high.
Exam tips
- Name what vibrates before giving the rule.
- Give two or three factors for each instrument class.
- Use "frequency" and "air column" correctly.
- For monotone, say "one steady pitch" with an example.
Practice questions on Musical Instruments and Monotone
Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.
Q1 · 1 mark · Very short answerBoard level
What is a monotone?
Hint
Single pitch.
Answer
A sound of a single, unchanging pitch.
Q2 · 2 marks · Short answerHarder board level
How does covering holes of a flute change the note?
Hint
Air column length.
Answer
Covering the lower holes lengthens the vibrating air column, giving a lower pitch; uncovering holes shortens it and raises the pitch.
Q3 · 3 marks · Short answerHarder board level
Why do guitars and sitars have a hollow wooden body?
Hint
Loudness.
Answer
The string alone sets little air in motion. The hollow body vibrates with the string and sets a larger amount of air vibrating, which makes the sound louder.
Q4 · 3 marks · Short answerHarder board level
Classify and state what vibrates in: sitar, shehnai, tabla, violin, whistle.
Hint
Three groups.
Answer
String: sitar, violin (strings vibrate). Wind: shehnai, whistle (air column vibrates). Membrane: tabla (stretched skin vibrates).
Q5 · 4 marks · Long answerHOTS / competency
Which of these is a monotone: (i) a tuning fork, (ii) a person reading in one unchanging pitch, (iii) a song, (iv) a siren with changing pitch? Explain, and say why a monotone is dull in speech.
Hint
Is the pitch constant?
Answer
(i) and (ii) are monotones: the pitch is steady. (iii) and (iv) change pitch. Speech and music have varying pitch, which makes them interesting and expressive; a monotone has no variation, so it sounds dull.
Test your recall
Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.
1.What vibrates in a flute?Show answer
The air column.
2.Tighter membrane gives?Show answer
Higher pitch.
3.Thin string gives?Show answer
Higher pitch.
4.What is a monotone?Show answer
A sound of one steady pitch.
5.Shorter air column gives?Show answer
Higher pitch.
Musical Instruments and Monotone: frequently asked questions
What affects the pitch of a string instrument?
The length, tension and thickness of the string: a shorter, tighter or thinner string has a higher pitch.
Why does a jal tarang bottle with more water give a higher note?
More water means a shorter column of air above it, and a shorter air column vibrates faster, giving a higher pitch.
What is a monotone?
A monotone is a sound of a single, unchanging pitch, like a tuning fork note or a dial tone.