PhysicsICSE Class 10 · Loudness, Pitch and Quality of Sound

Pitch and Frequency: Shrill and Grave Sounds Explained (ICSE Class 10)

Updated 15 October 2026 · Fact-checked

Pitch is the characteristic of sound by which we tell a shrill (high) note from a grave (low) one. It depends on frequency: the higher the frequency, the higher the pitch. Pitch is subjective (a sensation); frequency is objective, measured in hertz. A shorter, tighter or thinner string, or a shorter air column, gives a higher pitch.

Count the waves in the same time: more waves means higher frequency and higher pitch, whatever the loudness or wave height.

Illustration drawn for QuestionBuddy.

Understand Pitch and Frequency of Sound

Three characteristics of a musical sound. We describe any sound by its loudness, its pitch and its quality (timbre). Each is linked to a measurable property of the wave: loudness to amplitude, pitch to frequency, quality to waveform. This page is about pitch.

What pitch is. Pitch is the characteristic of sound that lets us distinguish a shrill (high-pitched) sound from a grave or flat (low-pitched) one, even when both are equally loud. A whistle, a bird's chirp or a mosquito's whine is shrill; a lion's roar, a drum or a ship's horn is grave.

Pitch depends on frequency. The more vibrations the source makes per second, the higher the pitch:

$higher frequency \Rightarrow higher pitch .$

A note an octave higher has twice the frequency.

Subjective and objective. Pitch is a sensation, so it is subjective: it is judged by the ear. Frequency is objective: it can be measured with instruments, in hertz (Hz), and does not depend on the listener. Saying 'the frequency is shrill' or 'the pitch is 500 Hz' mixes the two ideas.

Pitch does not depend on loudness. A mosquito's buzz is faint but shrill (high frequency, small amplitude). A lion's roar is loud but grave (low frequency, large amplitude). Voices of women and children usually have a higher pitch than men's because their vocal cords are shorter and thinner and vibrate faster.

How to change the pitch of a stretched string. The natural frequency of a string, and so its pitch, increases when:

its vibrating length is reduced (pressing on a fret of a guitar or sitar);
its tension is increased (turning the tuning peg);
it is thinner (less mass per unit length): the thin strings of a guitar give the high notes.

Air columns. In a flute, a whistle or a bottle, an air column vibrates. A shorter air column gives a higher frequency. As a bottle is filled with water, the air column above the water shortens and the pitch of the sound rises. It is the air column, not the water column, whose length matters.

Frequency from a displacement–time graph. The time for one complete wave is the period $T$ :

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

If $n$ complete waves fit in time $t$ , then $T = \frac{t}{n}$ and $f = \frac{n}{t}$ . More waves packed into the same time means a higher frequency and a higher pitch. On a graph, the horizontal spacing (period) tells you the pitch; the height (amplitude) tells you the loudness.

Range of hearing. Human ears hear roughly 20 Hz to 20 kHz. In air at 340 m/s this is a wavelength range from $\frac{340}{20} = 17$ m down to $\frac{340}{20 000} = 1.7$ cm. Below 20 Hz is infrasonic, above 20 kHz ultrasonic.

Pitch and Frequency of Sound: formulas and key facts

Frequency and period: $f = \frac{1}{T} = \frac{n}{t}$; n complete waves in time t.
Wavelength in air: $λ = \frac{v}{f}$; Higher pitch, shorter wavelength in the same medium.
Pitch rule: $higher f \Rightarrow higher pitch$; Pitch is subjective; frequency is objective.
Raising the pitch: String shorter length
String greater tension
String thinner (lighter)
Air column shorter; Each raises the natural frequency.

String	shorter length
String	greater tension
String	thinner (lighter)
Air column	shorter

How to solve Pitch and Frequency of Sound questions

Pitch questions ask you to compare sounds, read a graph, or say how to change an instrument's note.

1Name the characteristic asked for: pitch (not 'frequency' or 'wavelength') when the question says 'characteristic of sound'.
2To compare pitch, compare frequencies; from a graph, compare periods (shorter period, higher pitch).
3From a graph, find $T$ from the time for one wave (or $\frac{t}{n}$ ), then $f = \frac{1}{T}$ ; convert ms to s.
4To raise the pitch of a string, say 'increase the tension' (or shorten the vibrating length, or use a thinner string).
5For air columns, refer to the length of the air column, not the water column.

Pitch and Frequency of Sound 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.

Tuning a guitar

Suppose your guitar's top string sounds slightly lower than the note from a tuner app.

What should you do to the tuning peg, and why does it work?

Try it first, then show the solutionSolution

A note that is too low has too small a frequency.
Turn the peg to increase the tension; a tighter string has a higher natural frequency, so the pitch rises to match.

Answer: Tighten the string (increase its tension) to raise its frequency and pitch.

Memory hook: Tight is bright, slack is flat.

Playing notes on a flute

Imagine you play a bamboo flute. With all the finger holes closed you get the lowest note; as you lift fingers off the holes one by one, starting from the far end, the notes climb higher.

Why does lifting fingers raise the pitch?

Try it first, then show the solutionSolution

The note comes from the air column inside the flute, which vibrates between the mouth hole and the first open hole.
Opening a hole nearer the mouth hole shortens this vibrating air column; a shorter air column has a higher natural frequency, so the pitch rises.

Answer: Each open hole shortens the vibrating air column, raising its frequency and pitch.

Memory hook: Open a hole, shorten the air, raise the note.

Tricks to remember Pitch and Frequency of Sound

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

Pitch is frequency's feeling
Frequency is the fact (Hz, measured); pitch is the feeling (shrill or grave).
Use it when: Subjective vs objective.
Mosquito and lion
Mosquito: small and shrill. Lion: loud and low. Pitch and loudness are independent.
Use it when: Separating pitch from loudness.
Short, Tight, Thin sings high
Shorter length, greater tension, thinner string: all raise the pitch.
Use it when: Changing the pitch of a string.
Graph reading
Across for pitch (period), up for loudness (amplitude), shape for quality.
Use it when: Displacement–time graph questions.

Pitch and Frequency of Sound: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Shrill or grave · 1 mark · MCQBoard level

A sound is described as shrill. This means it has a:
(a) large amplitude
(b) high frequency
(c) long wavelength in air
(d) complex waveform

Try it first, then show the solutionSolution

Shrill means high pitch, which means high frequency (and so a short wavelength in air).

Answer: (b) high frequency

Example 2: Pitch and frequency compared · 3 marks · Short answerBoard level

(a) Define pitch. (b) On what does it depend? (c) Why is pitch called subjective but frequency objective?

Try it first, then show the solutionSolution

(a) Pitch is the characteristic of sound by which a shrill sound is distinguished from a grave sound. (1)
(b) On the frequency: the higher the frequency, the higher the pitch. (1)
(c) Pitch is a sensation judged by the listener's ear; frequency is the number of vibrations per second, which can be measured by instruments independent of the listener. (1)

Answer: (a) Distinguishes shrill from grave (b) Frequency (c) Pitch is a sensation; frequency is measurable

Example 3: Frequency from a trace · 3 marks · Short answerHarder board level

On an oscilloscope trace of a note, 4 complete waves occupy 5 ms. Find (a) the period, (b) the frequency, (c) the wavelength of the note in air where sound travels at 340 m/s.

Try it first, then show the solutionSolution

(a) $T = \frac{5}{4} = 1.25$ ms $= 1.25 \times 1 0^{- 3}$ s. (1)
(b) $f = \frac{1}{1.25 \times 1 0 ^{- 3}} = 800$ Hz. (1)
(c) $λ = \frac{340}{800} = 0.425$ m. (1)

Answer: (a) 1.25 ms (b) 800 Hz (c) 0.425 m

Example 4: Limits of hearing · 2 marks · Short answerHarder board level

Humans hear frequencies from about 20 Hz to 20 kHz. Taking the speed of sound in air as 340 m/s, find the longest and shortest wavelengths we can hear.

Try it first, then show the solutionSolution

Longest (20 Hz): $λ = \frac{340}{20} = 17$ m. (1)
Shortest (20 kHz): $λ = \frac{340}{20 000} = 0.017$ m $= 1.7$ cm. (1)

Answer: 17 m and 1.7 cm

Example 5: A row of bottles · 3 marks · Short answerHarder board level

Five identical bottles hold different depths of water. A child blows across the mouth of each in turn to play a tune. (a) Which part vibrates to make each note? (b) Which bottle gives the highest note: the one with the most water or the least? (c) Explain your answer.

Try it first, then show the solutionSolution

(a) The air column above the water in each bottle. (1)
(b) The bottle with the most water. (1)
(c) The most water leaves the shortest air column, and a shorter air column has a higher natural frequency, so its note has the highest pitch. (1)

Answer: (a) The air column (b) The bottle with the most water (c) Shortest air column, highest frequency

Example 6: Tightening a wire · 4 marks · Short answerHOTS / competency

A trace of the note from a stretched wire shows one complete wave PR spanning 4 divisions, each division being 0.5 ms. (a) Find the frequency. (b) After the player adjusts the wire, one wave takes 1.6 ms. Find the new frequency. (c) What adjustment did the player make? (d) Name the characteristic of sound that changed.

Try it first, then show the solutionSolution

(a) $T = 4 \times 0.5 = 2$ ms, so $f = \frac{1}{2 \times 1 0 ^{- 3}} = 500$ Hz. (1)
(b) $f = \frac{1}{1.6 \times 1 0 ^{- 3}} = 625$ Hz. (1)
(c) The period became shorter (frequency higher), so the tension was increased (or the vibrating length shortened). (1)
(d) Pitch. (1)

Answer: (a) 500 Hz (b) 625 Hz (c) Increased the tension (d) Pitch

Example 7: Case study: a sitar player · 4 marks · Case-basedHOTS / competency

A sitar player plays the same string in three ways: (i) open, (ii) pressed at a fret halfway along, (iii) open but after turning the peg to loosen it.
(a) In which case is the pitch highest? Why?
(b) What happens to the pitch in (iii) compared with (i)?
(c) If the open string gives 262 Hz, what would you expect the frequency to be if its vibrating length were exactly halved (the note an octave higher)?
(d) Does plucking harder change the pitch? Explain.

Try it first, then show the solutionSolution

(a) (ii): a shorter vibrating length gives a higher frequency, hence a higher pitch. (1)
(b) Lower: reduced tension lowers the frequency. (1)
(c) An octave higher is twice the frequency: 524 Hz. (1)
(d) No: plucking harder increases the amplitude (loudness), not the frequency. (1)

Answer: (a) (ii), shorter length (b) Lower (c) 524 Hz (d) No, only loudness changes

Where students lose marks in Pitch and Frequency of Sound

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

Mistake: Not linking the period on a graph to frequency
The horizontal length of one complete wave on a displacement–time graph is the period, and f = 1/T.
Wrong working
Treating the length PR as the wavelength or amplitude.
Right working
'PR is one period; a shorter PR means a higher frequency.'
Do this: Label T on every trace before answering.
Usually costs: Reported by CISCE examiners for 2025 Q2(iii).
Mistake: Vague ways of changing pitch
The expected answer names the physical quantity: tension.
Wrong working
'Tighten the wire with the hand', 'increase the weight' or 'reduce the wavelength'.
Right working
'Increase the tension in the wire.'
Do this: Use the words tension, length, thickness.
Usually costs: Reported by CISCE examiners for 2025 Q2(iii).
Mistake: Giving a quantity instead of a characteristic
The characteristics of sound are loudness, pitch and quality; frequency and wavelength are wave quantities.
Wrong working
'The characteristic that changes is frequency.'
Right working
'Pitch.'
Do this: Characteristic → loudness, pitch or quality only.
Usually costs: Also reported for 2025 Q2(iii).
Mistake: Water column instead of air column
The air above the water vibrates; its length decides the frequency.
Wrong working
Accepting 'frequency is inversely proportional to the water column'.
Right working
'Frequency increases as the air column shortens.'
Do this: Read assertion and reason separately, word by word.
Usually costs: Reported by CISCE examiners for 2025 Q1(xi).

Exam tips

Use 'shrill' and 'grave' in definitions of pitch; examiners look for them.
In graph questions, change only one feature at a time: spacing for pitch, height for loudness.
When asked how to raise the pitch of a string, 'increase the tension' is the expected answer; also accept shortening the vibrating length.
Keep loudness and pitch apart: a loud sound is not necessarily high-pitched.

Practice questions on Pitch and Frequency of Sound

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 · MCQBoard level
The pitch of a stretched string can be raised by:
(a) plucking it harder
(b) increasing its tension
(c) using a thicker string
(d) increasing its length
Hint
Which change raises the frequency?
Answer
(b) increasing its tension
Q2 · 1 mark · Very short answerBoard level
Which characteristic of a sound changes when its frequency is changed?
Hint
Shrill or grave.
Answer
Pitch.
Q3 · 2 marks · Short answerHarder board level
A mosquito's wings beat about 500 times per second. Find the period of the wingbeat in ms, and explain why its sound is shrill but faint.
Hint
$T = \frac{1}{f}$ ; loudness depends on amplitude.
Answer
$T = \frac{1}{500} = 2 \times 1 0^{- 3}$ s $= 2$ ms. The high frequency gives a high pitch (shrill), but the tiny wings have a small amplitude and area, so the sound is faint.
Q4 · 2 marks · Short answerBoard level
One complete wave of a note takes 0.8 ms on a trace. Find its frequency and state whether its pitch is higher or lower than that of a 1 kHz note.
Hint
Convert ms to s.
Answer
$f = \frac{1}{0.8 \times 1 0 ^{- 3}} = 1250$ Hz, which is higher than 1 kHz, so its pitch is higher.
Q5 · 2 marks · Short answerHarder board level
Why do the voices of women and children usually have a higher pitch than those of men?
Hint
Vocal cords.
Answer
Their vocal cords are shorter and thinner, so they vibrate with a higher frequency; a higher frequency gives a higher pitch.
Q6 · 3 marks · Short answerHarder board level
Two notes have frequencies 262 Hz and 524 Hz. (a) Find the ratio of their frequencies. (b) Find their periods in ms. (c) Which sounds more shrill?
Hint
Octave.
Answer
(a) $524 : 262 = 2 : 1$ (an octave). (b) $\frac{1}{262} \approx 3.82$ ms; $\frac{1}{524} \approx 1.91$ ms. (c) The 524 Hz note (higher frequency).
Q7 · 1 mark · Assertion-reasonHarder board level
Assertion (A): A thin guitar string gives a higher note than a thick string of the same length under the same tension.
Reason (R): A thinner string has a smaller mass per unit length, so its natural frequency is higher.
(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.
Hint
Mass per unit length and frequency.
Answer
(a) Both are true, and (R) explains (A): the higher natural frequency gives the higher pitch.
Q8 · 3 marks · Short answerHOTS / competency
A microphone shows 30 complete waves of a whistle's note in 0.025 s. (a) Find its frequency. (b) Find its wavelength in air (speed 336 m/s). (c) The whistle is blown harder and the trace becomes taller, but 30 waves still take 0.025 s. What has changed and what has not?
Hint
Height vs spacing.
Answer
(a) $f = \frac{30}{0.025} = 1200$ Hz. (b) $λ = \frac{336}{1200} = 0.28$ m. (c) The amplitude (loudness) has increased; the frequency and pitch are unchanged.
Q9 · 2 marks · Short answerHarder board level
A student says: 'To raise the pitch of a guitar string, reduce its wavelength.' Explain why this answer would not earn the mark and give a correct instruction.
Hint
What can the player actually change?
Answer
The player cannot set the wavelength directly; the pitch depends on the string's frequency, which is changed through its tension, length or thickness. Correct: 'increase the tension of the string' (or 'shorten its vibrating length').

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.Pitch depends on?Show answer
Frequency.
2.Is pitch subjective or objective?Show answer
Subjective.
3.Effect of increasing tension on a string's pitch?Show answer
It rises.
4.As a bottle fills with water, the pitch…Show answer
Rises (the air column shortens).
5.Frequency of a note an octave higher?Show answer
Double.

Pitch and Frequency of Sound: frequently asked questions

What is the relation between pitch and frequency?

Pitch depends on frequency: the higher the frequency of a sound, the higher (more shrill) its pitch. Frequency is measured in hertz, while pitch is how the ear perceives it.

How can the pitch of a string be increased?

By increasing its tension, shortening its vibrating length or using a thinner string. Each of these raises the string's natural frequency.

Why does the pitch rise as a bottle is filled with water?

The air column above the water vibrates. As the bottle fills, this air column gets shorter, its natural frequency rises, and so the pitch rises.