PhysicsICSE Class 8 · Sound

Frequency, Pitch, Amplitude and Loudness of Sound (ICSE Class 8 Physics)

Updated 17 October 2026 · Fact-checked

Sound is produced by vibrations. Frequency is the number of vibrations per second (hertz); higher frequency means higher pitch. Amplitude is the largest distance a vibrating body moves from rest; larger amplitude means louder sound, measured in decibels (dB). Pitch and loudness are independent.

Understand Frequency, Pitch, Amplitude and Loudness

All sounds come from vibrations: a guitar string, a drum skin, the air in a flute, our vocal cords.

Frequency and pitch.
$frequency = \frac{number of vibrations}{time in seconds}$

Unit: hertz (Hz); 1 Hz = 1 vibration per second.

Pitch tells a shrill (high) sound from a deep (low) one.

Higher frequency, higher pitch: whistle, bird's chirp, a child's voice, a mosquito's whine.
Lower frequency, lower pitch: lion's roar, a man's deep voice, a large drum.

Amplitude and loudness. Amplitude is the greatest distance a vibrating body moves from its rest position.

Larger amplitude, louder sound (strike a drum harder).
Loudness falls as you move away from the source.

Decibels. Loudness is measured in decibels (dB). Rough levels: whisper or rustling leaves about 20 to 30 dB, normal conversation about 60 dB, heavy traffic about 80 to 90 dB. Long exposure above about 85 dB can damage hearing. Very loud sound is noise pollution.

Independent. Pitch depends on frequency, loudness on amplitude. You can sing the same note softly or loudly (same pitch, different loudness), or a high and a low note equally loudly.

	Pitch	Loudness
Depends on	frequency	amplitude
Unit	hertz (frequency)	decibel
Changes when	vibrations per second change	the size of vibration changes

Frequency, Pitch, Amplitude and Loudness: formulas and key facts

Frequency: $f = \frac{vibrations}{time (s)}$; Hertz (Hz) = vibrations per second.
Pitch and frequency: $higher f \Rightarrow higher pitch$; Shrill sound = high frequency.
Loudness and amplitude: $larger amplitude \Rightarrow louder$; Measured in dB.

How to solve Frequency, Pitch, Amplitude and Loudness questions

Find frequency from counts and time, then relate it to pitch; relate amplitude to loudness separately.

1Convert time to seconds.
2Frequency = number of vibrations ÷ time.
3Compare frequencies for pitch: the larger is shriller.
4Compare amplitudes for loudness; do not use frequency for loudness.
5Give the unit: Hz for frequency, dB for loudness.

Frequency, Pitch, Amplitude and Loudness 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.

Mosquito and bee

Suppose a mosquito's wings make 3000 vibrations in 5 s and a bee's wings make 1250 vibrations in 5 s.

Find each frequency and say whose sound is shriller.

Try it first, then show the solutionSolution

Mosquito: $\frac{3000}{5} = 600$ Hz.
Bee: $\frac{1250}{5} = 250$ Hz.
The mosquito has the higher frequency.

Answer: 600 Hz and 250 Hz; the mosquito's sound is shriller.

Memory hook: More vibrations per second, higher pitch.

Hard and soft strikes

Imagine you strike a drum softly and then hard.

What changes: pitch or loudness?

Try it first, then show the solutionSolution

The skin vibrates through a larger distance when struck hard: larger amplitude.
The number of vibrations per second stays the same, so the pitch is unchanged.

Answer: Loudness increases; pitch stays the same.

Memory hook: Hard hit, big swing, loud.

Tricks to remember Frequency, Pitch, Amplitude and Loudness

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

Pitch = frequency
High f, high pitch; low f, low pitch.
Use it when: Pitch.
Loud = large amplitude
Larger swings make louder sound.
Use it when: Loudness.
Hertz is per second
Hz = 1/s: count the vibrations in one second.
Use it when: Unit.

Frequency, Pitch, Amplitude and Loudness: solved examples

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

Example 1: Frequency · 1 mark · MCQBoard level

A string makes 440 vibrations in 2 s. Its frequency is:
(a) 880 Hz
(b) 220 Hz
(c) 442 Hz
(d) 2 Hz

Try it first, then show the solutionSolution

$f = \frac{440}{2} = 220$ Hz.

Answer: (b) 220 Hz

Example 2: Pitch versus loudness · 2 marks · Short answerBoard level

Distinguish between pitch and loudness of a sound, stating what each depends on.

Try it first, then show the solutionSolution

Pitch: how shrill or deep a sound is; depends on frequency. (1)
Loudness: how loud or soft; depends on amplitude (and is measured in dB). (1)

Answer: Pitch ∝ frequency; loudness ∝ amplitude.

Example 3: Wings and frequency · 3 marks · Short answerHarder board level

A mosquito's wings make 3000 vibrations in 5 s, and a bee's make 1250 in 5 s. (a) Find each frequency. (b) Which sound has the higher pitch? (c) How many vibrations does the mosquito's wing make in 1 minute?

Try it first, then show the solutionSolution

(a) $\frac{3000}{5} = 600$ Hz; $\frac{1250}{5} = 250$ Hz. (1)
(b) The mosquito. (1)
(c) $600 \times 60 = 36000$ . (1)

Answer: (a) 600 Hz and 250 Hz (b) mosquito (c) 36 000

Example 4: Two tuning forks · 3 marks · Short answerHarder board level

Fork A makes 500 vibrations in 2 s; fork B makes 1000 vibrations in 2 s. Find the frequencies and the ratio. Which one has the higher pitch? If A is struck harder, what changes?

Try it first, then show the solutionSolution

A: $\frac{500}{2} = 250$ Hz; B: $\frac{1000}{2} = 500$ Hz. (1)
Ratio $f_{B} : f_{A} = 2 : 1$ ; B has the higher pitch. (1)
Struck harder, A's amplitude increases so it is louder; its frequency (pitch) does not change. (1)

Answer: A 250 Hz, B 500 Hz; B higher pitch; loudness increases for A

Example 5: Safe or risky? · 4 marks · Case-basedHOTS / competency

A student records these sound levels: a whisper 25 dB, ordinary conversation 60 dB, heavy traffic 85 dB, a loud speaker at a procession 105 dB. (a) Which can damage hearing on long exposure (above about 85 dB)? (b) Name this kind of sound pollution. (c) State two ways to reduce its effects. (d) Is a shriller sound always louder?

Try it first, then show the solutionSolution

(a) The 105 dB speaker (traffic is at the border and risky if long). (1)
(b) Noise pollution. (1)
(c) Lower the volume; keep away from the source; use ear protection. (1)
(d) No: pitch depends on frequency and loudness on amplitude, so they are independent. (1)

Answer: (a) loud speaker (b) noise pollution (c) lower volume, distance, ear protection (d) no

Where students lose marks in Frequency, Pitch, Amplitude and Loudness

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

Mistake: Mixing pitch and loudness
Loudness depends on amplitude, pitch on frequency.
Wrong working
"A louder sound has a higher pitch."
Right working
"A louder sound has a larger amplitude; pitch depends on frequency."
Do this: Use the two quantities separately.
Mistake: Forgetting to divide by time
Frequency is vibrations per second.
Wrong working
"600 vibrations in 3 s: 600 Hz."
Right working
" $\frac{600}{3} = 200$ Hz."
Do this: Divide by seconds.
Mistake: Wrong unit
Loudness is dB, frequency Hz.
Wrong working
"Loudness in Hz."
Right working
"Loudness in dB."
Do this: Pair each unit with its quantity.

Exam tips

Write f = vibrations ÷ time and show the unit Hz.
Use the pairs: frequency-pitch, amplitude-loudness.
Give the decibel scale numbers 20-30, 60, 80-90.
Mention noise pollution with loud sounds.

Practice questions on Frequency, Pitch, Amplitude and Loudness

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
Name the unit of frequency and the unit of loudness.
Hint
Two units.
Answer
Hertz (Hz) and decibel (dB).
Q2 · 2 marks · Short answerHarder board level
A tuning fork has a frequency of 256 Hz. How many vibrations does it make in half a second, and how long does it take for 1024 vibrations?
Hint
Hz means vibrations per second.
Answer
In 0.5 s: $256 \times 0.5 = 128$ vibrations. Time for 1024: $\frac{1024}{256} = 4$ s.
Q3 · 3 marks · Short answerHarder board level
Why is a lion's roar deep and a mosquito's hum shrill?
Hint
Frequency decides pitch.
Answer
The lion's vocal cords vibrate slowly (low frequency), giving low pitch. A mosquito's wings vibrate very rapidly (high frequency), giving high pitch.
Q4 · 2 marks · Short answerHarder board level
A girl sings the same note first softly and then loudly. State what changes and what stays the same, naming the physical quantities.
Hint
Amplitude and frequency.
Answer
Amplitude increases, so loudness (in dB) increases; frequency stays the same, so pitch is unchanged.
Q5 · 4 marks · Long answerHOTS / competency
Source P makes 1800 vibrations in 6 s; source Q makes 600 vibrations in 6 s. Compare frequencies and pitch. Can you say which is louder?
Hint
Frequency does not tell loudness.
Answer
$f_{P} = \frac{1800}{6} = 300$ Hz; $f_{Q} = \frac{600}{6} = 100$ Hz. P has three times the frequency of Q, so a higher pitch. Loudness depends on amplitude, which is not given, so we cannot say which is louder.

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.Unit of frequency?Show answer
Hertz (Hz).
2.Pitch depends on?Show answer
Frequency.
3.Loudness depends on?Show answer
Amplitude.
4.Unit of loudness?Show answer
Decibel (dB).
5.Sound level above which hearing may be damaged?Show answer
About 85 dB.

Frequency, Pitch, Amplitude and Loudness: frequently asked questions

What is frequency?

Frequency is the number of complete vibrations a source makes in one second, measured in hertz (Hz).

What is the difference between pitch and loudness?

Pitch depends on the frequency of vibration and tells how shrill the sound is. Loudness depends on the amplitude and is measured in decibels.

What is noise pollution?

Noise pollution is very loud or unwanted sound that can harm hearing and health; exposure above about 85 dB for long periods can damage hearing.