Loudness, Pitch and Quality of Sound ICSE Class 10: Characteristics of Sound

What Loudness, Pitch and Quality of Sound is about

Weightage: CISCE publishes no chapter or unit weightage for ICSE Physics. Loudness, Pitch and Quality of Sound is in the 3. Sound (iii) part of the 2027 syllabus and can be asked in both Section A and Section B of the 80-mark paper.Source: CISCE ICSE Physics (Science Paper 1) syllabus, examination year 2027

Key concepts

Loudness and its factors

Loudness is the sensation that lets us tell a loud sound from a faint one. It is subjective: it depends on the listener's ear as well as the sound.

Loudness increases with:

• amplitude of vibration (loudness is roughly proportional to the square of the amplitude; doubling the amplitude makes the intensity four times);
• surface area of the vibrating body (a big drum is louder than a small one);
• closeness to the source (intensity falls as the square of the distance);
• density of the medium;
• resonating bodies nearby (sound boxes).

Worked example

If the amplitude of vibration of a sound source is doubled, how does the intensity change?

Try it first, then show the solutionSolution

1. Intensity is proportional to the square of the amplitude.
2. $2^2=4$: the intensity becomes four times as large.

Answer: Four times

Intensity and the decibel

Intensity is the sound energy passing per second through unit area held perpendicular to the direction of the sound (unit W m⁻²). It is objective: it can be measured by an instrument, whatever the listener.

Loudness depends on intensity, but also on the sensitivity of the ear (which is greatest for frequencies around 2–4 kHz).

Sound level is expressed in decibels (dB). Typical levels: rustling leaves about 10–20 dB, whisper about 30 dB, normal conversation about 60 dB, busy traffic about 80–90 dB, a jet engine nearby about 120 dB or more (painful).

Worked example

A sound-level monitor reads 60 dB in a classroom and 90 dB near a busy road. Which is louder, and is the decibel a measure of frequency?

Try it first, then show the solutionSolution

1. The road (90 dB) has the higher sound level, so it is louder.
2. The decibel measures sound level (related to intensity), not frequency.

Answer: The road; no, dB measures sound level

Pitch and frequency

Pitch is the sensation by which we distinguish a shrill (high) sound from a grave (flat, low) one. It depends on the frequency: the higher the frequency, the higher the pitch.

Examples: a mosquito's buzz (high frequency, high pitch) vs a lion's roar (low pitch, though louder); women's and children's voices usually have a higher pitch than men's.

Pitch is subjective; frequency is objective (measured in hertz).

Worked example

The buzz of a mosquito is faint but shrill; the roar of a lion is loud but grave. Compare their pitch and loudness.

Try it first, then show the solutionSolution

1. Mosquito: high frequency, so high pitch; small amplitude, so less loud.
2. Lion: low frequency, so low pitch; large amplitude, so louder.

Answer: Mosquito: higher pitch, less loud; lion: lower pitch, louder

Changing the pitch of a string or air column

For a stretched string, the frequency (and so the pitch) increases when:

• the vibrating length is reduced (pressing the string against a fret);
• the tension is increased (turning the tuning peg);
• the string is thinner or lighter.

For an air column (flute, bottle), a shorter column gives a higher pitch.

Worked example

A guitarist wants a higher note from the same string. Give two ways.

Try it first, then show the solutionSolution

1. Press the string on a fret to shorten its vibrating length.
2. Or turn the peg to increase its tension.

Answer: Shorter vibrating length; greater tension

Quality (timbre) and waveform

Quality (timbre) lets us distinguish two sounds of the same loudness and pitch from different sources, such as a piano and a flute playing the same note, or two friends' voices.

It depends on the waveform: a real source vibrates at its main (fundamental) frequency together with weaker higher frequencies (overtones); the number and relative strengths of the overtones decide the shape of the wave and so the quality.

A tuning fork gives an almost pure (sine-shaped) note; a violin gives a complex waveform.

Worked example

How can you recognise a friend's voice on the phone without seeing them?

Try it first, then show the solutionSolution

1. Every voice has its own mixture of overtones.
2. This gives it a characteristic waveform, i.e. quality, which we recognise.

Answer: By the quality (timbre) of the voice

Reading displacement–time graphs

On a displacement–time graph of a sound wave:

• the height of a crest from the centre line is the amplitude → loudness;
• the time for one complete wave is the period $T$, and $f=\frac{1}{T}$ → pitch;
• the shape of the wave → quality.

A shorter period means a higher frequency and a higher pitch. To shorten the period of a string's note, increase its tension (or reduce its length).

Worked example

On a displacement–time graph, one complete vibration takes 4 ms. Find the frequency and the wavelength in air ($v=340$ m/s).

Try it first, then show the solutionSolution

1. $f=\frac{1}{4\times 10^{-3}}=250$ Hz.
2. $\lambda =\frac{340}{250}=1.36$ m.

Answer: 250 Hz; 1.36 m

Noise and noise pollution

Music is a pleasant sound with a regular waveform; noise is an unpleasant sound with an irregular waveform. Noise pollution is unwanted sound loud enough to harm health or comfort.

Effects: headaches, stress, sleeplessness, high blood pressure, loss of concentration and, with long exposure above about 80–85 dB, permanent hearing damage.

Control: silencers on vehicles, banning loud horns near hospitals and schools, sound-proofing, planting trees along roads, keeping loudspeaker volumes low, and wearing ear protection near loud machines.

Worked example

Give two harmful effects of noise pollution and two ways to reduce it near a highway.

Try it first, then show the solutionSolution

1. Effects: sleeplessness and stress; hearing damage over time.
2. Reduce: plant rows of trees as a sound barrier; enforce silencers and no-horn zones.

Answer: As listed

Physics in real life: Loudness, Pitch and Quality of Sound

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.

Topics in this chapter

• Pitch and Frequency of Sound
• Loudness and Intensity of Sound
• Quality (Timbre) of Sound and Waveforms

Loudness, Pitch and Quality of Sound formula sheet

Frequency from a graph

$f=\frac{1}{T}$

T = time for one complete wave on a displacement–time graph.

Wave equation

$v=f\lambda$

Wavelength of a note in air.

Intensity and amplitude

$I\propto A^2$

Doubling amplitude → four times intensity.

Intensity and distance

$I\propto \frac{1}{d^2}$

Twice as far → one quarter the intensity.

Characteristic ↔ cause

$\text{loudness}\leftrightarrow A,\text{pitch}\leftrightarrow f,\text{quality}\leftrightarrow \text{waveform}$

Subjective ↔ objective.

Loudness, Pitch and Quality of Sound: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the board asks Loudness, Pitch and Quality of Sound

The question patterns to expect, and the method that works for each.

Tricks to remember Loudness, Pitch and Quality of Sound

Short memory aids. Say each one aloud once, then use it on a question the same day.

• A-F-W

  Loudness–Amplitude, Pitch–Frequency, Quality–Waveform (in the order L-P-Q).

  Use it when: Linking characteristics to causes.

• Mosquito high, lion low

  Pitch is not loudness: the faint mosquito is shrill, the loud lion is grave.

  Use it when: Separating pitch from loudness.

• Tight and short = high

  Tighter or shorter strings give higher notes.

  Use it when: Changing pitch.

• Feel vs measure

  Loudness and pitch are felt (subjective); intensity and frequency are measured (objective).

  Use it when: Subjective–objective questions.

Loudness, Pitch and Quality of Sound: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In the board paper this is a 10-mark question split into 3 + 3 + 4 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Loudness, Pitch and Quality of Sound

The slips examiners see most often, and what to write instead.

• ✗Mistake: Not linking the period to frequency

  CISCE examiners' comments, 2025: candidates could not relate the length PR (one period) on a displacement–time graph to the frequency of the wave.

  ✓Do this: Period T is the time for one wave; f = 1/T. A shorter period means a higher frequency.

  Usually costs: 1 mark.

• ✗Mistake: Vague way of changing pitch

  CISCE examiners' comments, 2025: candidates suggested physically 'tightening the wire' or 'increasing weight' instead of stating 'increase the tension', or said 'reduce the wavelength'.

  ✓Do this: Name the physical quantity: increase the tension (or decrease the length).

  Usually costs: 1 mark.

• ✗Mistake: Naming a quantity instead of a characteristic

  CISCE examiners' comments, 2025: asked which characteristic of sound was affected, candidates wrote frequency or wavelength instead of pitch.

  ✓Do this: Characteristics are loudness, pitch and quality; frequency, amplitude and waveform are their causes.

  Usually costs: 1 mark.

• ✗Mistake: Mixing up pitch and loudness

  Calling a loud sound 'high-pitched' confuses amplitude with frequency; the lion's roar is loud but low-pitched.

  ✓Do this: Pitch: high/low (frequency). Loudness: loud/soft (amplitude).

  Usually costs: 1 mark.

• ✗Mistake: Treating the decibel as frequency

  The decibel is the unit of sound level, related to intensity; it is not a unit of frequency or pitch.

  ✓Do this: Hz for frequency; dB for sound level.

  Usually costs: 1 mark.

Practice questions on Loudness, Pitch and Quality of Sound

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   The characteristic of sound that distinguishes a shrill sound from a grave one is:
   (a) loudness
   (b) pitch
   (c) quality
   (d) intensity

   Hint

   Frequency-based.

   Answer

   (b)

2. Q2 · 1 mark · MCQBoard level

   The unit in which sound level is commonly expressed is:
   (a) hertz
   (b) watt
   (c) decibel
   (d) joule

   Hint

   Used by noise monitors.

   Answer

   (c)

3. Q3 · 1 mark · MCQHarder board level

   Two notes have the same frequency and amplitude but come from different instruments. They differ in:
   (a) pitch
   (b) loudness
   (c) quality
   (d) speed

   Hint

   Waveform.

   Answer

   (c)

4. Q4 · 1 mark · Assertion-reasonBoard level

   Assertion (A): A big drum produces a louder sound than a small drum struck with the same force.
   Reason (R): The larger vibrating surface sets a larger mass of air into vibration.
   (a) (A) is true and (R) is false.
   (b) (A) is false and (R) is true.
   (c) Both (A) and (R) are true, and (R) is the correct explanation for (A).
   (d) Both (A) and (R) are true, but (R) is not the correct explanation for (A).

   Hint

   Surface area.

   Answer

   (c)

5. Q5 · 2 marks · Very short answerHarder board level

   Fill in the blanks: (a) Loudness is a __________ (subjective / objective) quantity. (b) The pitch of a sound increases when its __________ increases.

   Hint

   Sensation; frequency.

   Answer

   (a) subjective (b) frequency

6. Q6 · 2 marks · Short answerHarder board level

   One vibration of a note takes 2.5 ms on a displacement–time graph. Find its frequency and compare its pitch with a note of 250 Hz.

   Hint

   f = 1/T.

   Answer

   $f=\frac{1}{0.0025}=400$ Hz; higher pitch than 250 Hz.

7. Q7 · 3 marks · Long answerBoard level

   State the characteristic of sound that depends on (a) amplitude, (b) frequency, (c) waveform, giving one example of each in daily life.

   Hint

   L, P, Q.

   Answer

   (a) Loudness: shouting vs whispering. (b) Pitch: mosquito vs lion. (c) Quality: telling a violin from a flute playing the same note.

8. Q8 · 3 marks · Long answerHarder board level

   A sitar string sounds too low. (a) Should the player increase or decrease its tension? (b) What happens to its frequency and period? (c) Name the characteristic of sound that changes.

   Hint

   Tighter is higher.

   Answer

   (a) Increase the tension. (b) Frequency increases, period decreases. (c) Pitch.

9. Q9 · 3 marks · Long answerHOTS / competency

   Explain why (a) the buzz of a mosquito is faint but shrill while a lion's roar is loud but grave, (b) a note on a piano and the same note on a guitar sound different.

   Hint

   Separate amplitude, frequency and waveform.

   Answer

   (a) The mosquito's wings vibrate at high frequency with small amplitude (high pitch, low loudness); the lion's vocal cords vibrate at low frequency with large amplitude (low pitch, high loudness). (b) The instruments produce different overtones, so the waveforms (quality) differ.

10. Q10 · 3 marks · Long answerHarder board level

    State three effects of noise pollution on human health and three ways to control it.

    Hint

    Health and measures.

    Answer

    Effects: hearing loss; stress/headaches; sleeplessness or high blood pressure. Control: silencers and no-horn zones; trees and sound barriers; limits on loudspeaker volume (and ear protection).

11. Q11 · 1 mark · MCQHOTS / competency

    If the distance from a sound source is halved, the intensity of the sound becomes:
    (a) half
    (b) double
    (c) four times
    (d) one quarter

    Hint

    I ∝ 1/d².

    Answer

    (c)

12. Q12 · 4 marks · Long answerHOTS / competency

    A microphone records two sounds. Sound X has crests twice as high as Y, and three complete waves of X fit in the time of one wave of Y. (a) Compare their loudness (as intensity). (b) Compare their frequencies and pitch. (c) If X's waveform is a smooth sine and Y's is jagged, what else differs?

    Hint

    Intensity ∝ A²; f = 1/T.

    Answer

    (a) X's intensity is $2^2=4$ times Y's: X is louder. (b) X's frequency is 3 times Y's: higher pitch. (c) Their quality (timbre) differs: X is a pure tone, Y has overtones.

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. 1.Loudness depends mainly on?Show answer

   Amplitude (intensity).

2. 2.Pitch depends on?Show answer

   Frequency.

3. 3.Quality depends on?Show answer

   Waveform (overtones).

4. 4.Unit of sound level?Show answer

   Decibel (dB).

5. 5.Is loudness subjective or objective?Show answer

   Subjective.

6. 6.How to raise the pitch of a string?Show answer

   Increase tension or decrease vibrating length.

7. 7.Intensity if amplitude is doubled?Show answer

   Four times.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you match each characteristic to its cause?
• ☐Can you read amplitude and period off a graph?
• ☐Can you state four factors affecting loudness?
• ☐Can you distinguish subjective and objective quantities?
• ☐Do you know typical dB levels and effects of noise?

Loudness, Pitch and Quality of Sound: frequently asked questions