Light waves and sound waves compared
Light and sound are both waves, which is why both reflect and both spread out. But one needs matter to travel through and one does not - and that single difference explains the thunderstorm, the vacuum and space.
Part of your national curriculum
- Physics: waves: Understand the similarities and differences between light waves and waves in matter, and frequencies of sound waves measured in hertz
Lesson overview
What you'll learn in this lesson
Understand the similarities and differences between light waves and waves in matter, and frequencies of sound waves measured in hertz
Key learning points
- • Both are waves
- • Frequency in hertz
- • A medium, or none
- • Speed, and what you notice
This lesson at a glance
- 30 minutes
- 19 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 19
Watch first
Light waves and sound waves compared
An English teaching video on this topic from Massimo Boscherini. Watch it, then scroll down for the lesson.
Do it for real
The practicals below use what the film shows, with a full method you can follow at home.
In a nutshell
Understand the similarities and differences between light waves and waves in matter, and frequencies of sound waves measured in hertz
What you already know
Part 2 of 19
Before we start
What you already know
You should know that light travels in straight lines and that sound is made by vibrations.
Key words
Part 3 of 19
Key words
Words you'll need today
- Wave
- A transfer of energy without transferring matter.
- Frequency
- Waves per second, measured in hertz (Hz).
- Amplitude
- The size of the vibration; it sets loudness or brightness.
- Longitudinal
- A wave that vibrates along the direction of travel, like sound.
- Transverse
- A wave that vibrates across the direction of travel, like light.
Learning cycle
Part 4 of 19
Learning cycle 1 of 2
What the two have in common
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 5 of 19
Learn
Both are waves
Both light and sound carry energy from place to place without carrying matter along - shout across a room and no air arrives at the other end. Both reflect, both refract when their speed changes, and both spread and weaken with distance. Both are described by frequency and amplitude: bigger amplitude means louder or brighter, higher frequency means higher pitch or bluer light.
Explore the idea
Part 6 of 19
Learn
Frequency in hertz
Frequency counts vibrations per second in hertz. A 440 Hz string vibrates 440 times a second and sounds as A above middle C. Human hearing runs roughly 20 Hz to 20 000 Hz, narrowing with age; above that is ultrasound, used in scanning and in bat echolocation. Double the frequency and the pitch rises by an octave.
Quick check
Part 7 of 19
Quick check
Which wave cannot travel through a vacuum?
Quick check
Part 8 of 19
Quick check
Frequency is measured in...
Reset break
Part 9 of 19
Pause
That's sitting 1 of 2 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 10 of 19
Learning cycle 2 of 2
Where they differ
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 11 of 19
Learn
A medium, or none
Sound is a longitudinal wave in matter: particles are squeezed together and pulled apart along the direction of travel, so sound cannot cross a vacuum. Light is a transverse electromagnetic wave and needs no medium at all, which is why we see the Sun but hear nothing from it. Ring a bell inside a jar and pump the air out: the sound fades to nothing while the bell stays perfectly visible.
Explore the idea
Part 12 of 19
Learn
Speed, and what you notice
Light travels about 300 000 000 m/s; sound about 330 m/s in air - roughly a million times slower. So you see lightning almost instantly and hear the thunder seconds later, about three seconds for every kilometre. Sound also travels faster in water and faster again in steel, because the particles are closer and pass the vibration on sooner - the opposite of what most people expect.
Quick check
Part 13 of 19
Quick check
Increasing the amplitude of a sound wave makes it...
Quick check
Part 14 of 19
Quick check
You see lightning before you hear thunder because...
Common mix-ups
Part 15 of 19
Common mix-ups
Things people often get wrong
- Sound needs a medium; light does not.
- Waves transfer energy, not matter.
- Amplitude sets loudness; frequency sets pitch.
- Sound travels faster in solids and liquids than in air, not slower.
Challenge round
Part 16 of 19
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 17 of 19
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Both light and sound carry energy from place to place without carrying ____ along - shout across a room and no air arrives at the other end.
Mastery quiz
Part 18 of 19
Marked quiz
End of lesson quiz: Light waves and sound waves compared
6 questions, marked with the reasoning shown. No timer.
1. Sound is which type of wave?
2. Human hearing covers roughly...
3. Sound travels fastest in...
4. A wave transfers...
5. Thunder heard 3 seconds after the flash means the storm is about...
6. Doubling a note's frequency raises its pitch by...
Lesson round-up
Part 19 of 19
Lesson round-up
Ready when you are
Quiz score
Not sat
Games
Not played
Points this lesson
0
Best run
0 in a row
Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaDo the work
Your written work for this lesson
This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.
Why the school greenhouse failed
A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.
The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.
The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.
Written for Good Learning Co.
Reading questions
- Name the variable the club changed the second time, and one variable they kept the same.
- Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
- Write a conclusion for the club's report, saying how far the evidence supports it.
Method and results
WritingWrite the aim, what you changed, what you measured and what you kept the same, then record your results in a table.
1 page + results table
Conclusion
WritingExplain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.
6–8 sentences
Labelled diagram
DiagramDraw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
ReadingRead the lesson text again and write the key ideas in your own words.
Half a page of notes
Saved as you type.
Part 1 of 19 · Watch & discover
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Understand the similarities and differences between light waves and waves in matter, and frequencies of sound waves measured in hertz