S3 Science | Sound and Waves: Frequency, Pitch and Ultrasound

S3 Science | Sound and Waves: Frequency, Pitch and Ultrasound — Tutor Prep Guide

2026-11-15

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Students know sound comes from vibration but confuse loud with high. This lesson separates frequency and amplitude into two independent axes and adds one echo calculation.

Objectives — Students can: (1) explain that sound comes from vibration and needs a medium, so it cannot travel through a vacuum; (2) use frequency in hertz to describe pitch and amplitude to describe loudness, and quote the hearing range of roughly 20 Hz to 20 kHz; (3) calculate distance from an echo using speed, time and a factor of two, and find wavelength as speed divided by frequency.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Vibration	How is sound produced?	A vibrating object creates a sound wave; the sound stops when vibration stops
Medium	Can sound travel through a vacuum?	No, sound needs particles to carry it
Prefixes	How many hertz is one kilohertz?	One kilohertz is 1,000 hertz

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-5 min	Feel your throat	Ask students to touch their throat while speaking	Say that sound comes from vibration and stops with it
5-17 min	Frequency and pitch	Pluck rulers of different lengths or play 170 Hz and 340 Hz	State that higher frequency means higher pitch
17-29 min	Amplitude and loudness	Keep frequency fixed and raise the volume	State that amplitude sets loudness, pitch unchanged
29-37 min	Echo and wavelength	Use 340 m/s to find the distance for a 0.6 s echo and the wavelength at 170 Hz	Get 102 m and 2 m, remembering to halve
37-42 min	Ultrasound uses	Bats, medical scans and sonar	Explain short wavelength gives fine detail
42-45 min	Exit check	Roughly what is the wavelength at 20 kHz?	About 0.017 m, that is 1.7 cm

03 Teaching script (read it out)

Scene 1: Sound is vibration, and it needs a medium

Begin with the body: touch the throat while speaking, then mouth the words silently, and the difference is immediate. Use a tuning fork or a plucked ruler to show that sound lasts only while the object vibrates. Then handle the medium with the bell jar demonstration or its description: as air is pumped out the sound fades to nothing, so a sound wave needs particles. This also clears the film myth of explosions in space. Students should be able to state three sentences unprompted: vibration makes sound, a medium carries it, a vacuum cannot.

Ask why sound cannot cross a vacuum and for one everyday example of a medium

Scene 2: Frequency and amplitude: two independent axes

This section removes the confusion that louder means higher. Fix the loudness and raise the frequency from 170 Hz to 340 Hz, and ask what changes: the pitch rises. Then fix the frequency and increase the amplitude: it gets louder while the pitch stays the same. Students should state the mapping themselves. Add the hearing range of 20 Hz to 20 kHz, naming infrasound below and ultrasound above. Compare wavelengths: 340 divided by 170 gives 2 m, while 340 divided by 20,000 gives 0.017 m, so higher frequency means shorter wavelength, a relationship reused for ultrasound and communications.

Ask what frequency and amplitude each control and have students compute the wavelength at 170 Hz

Scene 3: Echoes and ultrasound: halve the time

Echo questions have one trap: sound travels there and back, so distance is speed times time divided by two. For a 0.6 second echo at 340 m/s the round trip is 204 m and the one-way distance is 102 m. Ask students to justify the halving with a shout across a valley. Reverse it too: a wall 170 m away gives a 1 second echo. Then ultrasound at 40 kHz has a wavelength near 8.5 mm, short enough to resolve small structures, which is why medical scans and bats use it, while sonar uses lower frequencies to travel further. Finish by comparing speed in solids, liquids and gases: fastest in solids because particles are closest, which is why a train is heard through the rails first.

Ask why an echo is halved and for two advantages of short ultrasound wavelengths

04 Question types and worked steps

Type	Example	Steps	Answer
Frequency and pitch	Two tuning forks are at 256 Hz and 512 Hz. Which has the higher pitch?	1) Higher frequency means higher pitch. 2) Compare 256 and 512. 3) Name the fork and the reason	The 512 Hz fork, because its frequency is higher
Wavelength	The speed of sound is 340 m/s and the frequency is 170 Hz. What is the wavelength?	1) Wavelength is speed divided by frequency. 2) Divide 340 by 170. 3) Answer in metres	2 m
Echo distance	A shout returns from a cliff after 0.6 s. How far away is the cliff at 340 m/s?	1) The sound travels there and back. 2) 340 times 0.6 is 204 m. 3) Halve it	102 m
Comparing media	Does sound travel fastest in steel, water or air?	1) Closer particles carry sound faster. 2) Steel is a solid. 3) Order steel, then water, then air	Steel fastest, then water, then air

Sanity check (teach this): Three checks: echoes must be halved, so an answer of 204 m means the return trip was ignored; units must be hertz and metres with centimetres converted; and the magnitude must be sensible, since 20 kHz gives about 1.7 cm rather than 17 m, which reveals a divide by 20 instead of 20,000. One further check: frequency does not change the speed in a given medium, so wavelength and frequency are inversely related, which is a useful self-check.

05 Independent practice (3 questions)

Question	Answer	What to watch
Speed 340 m/s and frequency 340 Hz: what is the wavelength?	1 m	Answering 340 m means multiplication was used
An echo returns after 1 s at 340 m/s. How far is the wall?	170 m	Answering 340 m means the halving was forgotten
What does a larger amplitude change?	Loudness, not pitch	Answering higher pitch means amplitude and frequency are still mixed up

06 Common mistakes and what to say

Mistake	Student writes	Say this
Loud means high	A louder sound is a higher sound.	Loudness comes from amplitude, pitch from frequency. A sound can be loud and low.
Echo not halved	A 0.6 s echo at 340 m/s means 204 m away.	The sound travels both ways, so halve it to 102 m.
Sound in a vacuum	Explosions are heard in space, so sound needs no medium.	Sound needs particles; film sound effects are added later.
Wavelength proportional to frequency	Higher frequency means a longer wavelength.	At fixed speed, wavelength is speed divided by frequency, so higher frequency means shorter wavelength.

07 Homework (paper, section and question numbers)

Reflection and refraction, question 2 — Light and sound are both waves, so the frequency and wavelength link transfers
Forces and motion: speed and acceleration, question 2 — Distance equals speed times time, with one extra halving for echoes
Earth, Moon and the solar system, question 1 — Useful for correcting the sound in space myth

08 Exit check (last 5 minutes)

Question	Answer	Decision
What do frequency and amplitude control?	Frequency gives pitch, amplitude gives loudness	Answering both for loudness means the axes are not separated
A 0.6 s echo at 340 m/s: how far?	102 m	Answering 204 m means the halving was missed
What is the ultrasound range?	Above 20 kHz	Answering above 20 Hz confuses it with the hearing threshold

09 Tutor FAQ

Should students derive the wavelength equation?

At S3 they only need wavelength equals speed divided by frequency, checked with units. The derivation belongs to senior secondary waves.

How do I demonstrate frequency without a signal generator?

Glasses filled to different levels give different pitches; an online tone generator playing 170 Hz and 340 Hz works too. The point is same loudness, different pitch.

How many ultrasound uses should be memorised?

Two or three: bat echolocation, medical scanning, sonar. Marks come from the reason that short wavelengths resolve detail, not from a list.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.