Light is a transverse wave, and it is one small part of a family of electromagnetic waves: radio, microwave, infrared, visible light, ultraviolet, X-rays and gamma rays. They all travel at the same speed in a vacuum (300 000 km/s) and differ in frequency and wavelength. Higher frequency means a shorter wavelength and more energy, which decides what each is used for and how careful we must be with it.
A sunburn, a microwave oven, a TV remote and a hospital X-ray all use the same kind of wave. What makes them so different?
Sound needed particles to carry it. Light doesn't. This lesson meets the wave model for light and for its whole family.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: more energy
ExploreTry it on the board and compare what happens with your prediction.
Explore: the seven bands
Watch the wave at the bottom change: not to scale, but the pattern is real.
Try it yourselfYour edits are saved in this browser.
Click each of the seven bands, from Radio to Gamma, and read the details.
Use the board. This ticks when you get there.
Find the band that causes sunburn.
Use the board. This ticks when you get there.
Find the band used to look at bones.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: the wave model of light
In your book: draw a line with the seven bands from radio to gamma. Under it write 'longer wavelength, lower frequency, less energy' at one end and the opposite at the other, then add one use to each band.
Match each wave to a use.
Radio waves
Microwaves
Infrared
Ultraviolet
X-rays
Gamma rays
Elaborate TypicalUse the same idea in a new context.
Elaborate: choosing a wave
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Find the band with a wavelength of about 12 cm.
Use the board. This ticks when you get there.
Elaborate WiderUse the same idea in a new context.
Elaborate: sun safety
Elaborate TypicalUse the same idea in a new context.
Elaborate: Slip, Slop, Slap
In 1981 Cancer Council Victoria launched Slip, Slop, Slap: slip on a shirt, slop on sunscreen, slap on a hat. Seek shade and slide on sunglasses were added later.
Did it help Australians take up sun safety?
Strong evidence linking UV exposure to skin cancer
A short, catchy message with cheap, easy actions
'No hat, no play' rules in schoolsRules turn advice into a habit for a whole generation.
The UV Index in daily weather reports
UV feeling hot on the skin, so people notice itUV can't be felt as heat: that is exactly why people needed reminders.
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Light is a transverse wave and one part of the electromagnetic spectrum: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.
All travel at the same speed in a vacuum (300 000 km/s), with no medium needed.
Radio to gamma: shorter wavelength, higher frequency, more energy per wave.
Frequency decides use and risk: low-energy waves carry signals; high-energy waves can damage cells.
For teachers
Students describe light and the electromagnetic spectrum as transverse waves differing in frequency and wavelength, and link frequency to energy and use (AC9S9U04, node 4). About 26 minutes.
I can say what makes light and X-rays the same kind of wave.
I can say how wavelength, frequency and energy change from radio to gamma.
I can match a wave to a use and a risk.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider. It follows How does current flow? and comes before How does light bend?
The pattern is the point: wavelength down, frequency up, energy up. The wave at the bottom of the board is a schematic with a few cycles per band: the real wavelengths span about fifteen powers of ten. Figures are typical and rounded: radio 3 m (100 MHz), microwave 12 cm (2.5 GHz), infrared 10 µm, visible 500 nm, UV 100 nm, X-ray 1 nm, gamma 1 pm.
Be clear that 'more energy per wave' is different from 'more powerful': a strong radio transmitter delivers more power than a dim UV lamp, but each radio wave carries little energy.
Running the lesson
Engage: tally the predictions. Ask the 'microwaves' group what makes an oven powerful.
Explore: ask what pattern they notice from Radio to Gamma.
Explain: the energy question and the uses match are the success criteria.
In your own words: the labelled line of seven bands.
The hard part (on purpose)
Separating how powerful a source is from how much energy each wave carries. When a student says microwaves are more dangerous than X-rays because an oven cooks food, ask what each single wave can do to one cell.
When students get stuck
A student says gamma rays travel faster. Ask: Which of the two bands is it that differs in speed on the board? Fix: None: all travel at 300 000 km/s in a vacuum.
A student says light needs air to travel through. Ask: How does sunlight reach us? Fix: Across empty space. Light needs no medium.
A student thinks infrared is the same as visible light. Ask: Which band has the longer wavelength? Fix: Infrared. We feel it as heat but can't see it.
Stretch and support
Stretch: A radio wave has frequency 100 MHz and a speed of 300 000 000 m/s. What is its wavelength? (3 m, using speed = frequency × wavelength.)
Support: Give the seven bands on cards in order with their names and ask students to add 'long', 'short' and arrows for frequency and energy before they try the match.
Where it leads
Next: How does light bend? uses the wave model to explain reflection and refraction.
In class: a prism or a CD to show visible light spreading; a TV remote seen through a phone camera (infrared); UV beads that change colour in sunlight; discuss local sun-safety rules.
What each step is for
Engage: more energy: Students rank by familiarity or by 'power' (microwaves heat food). Frequency, not the device, sets the energy of each wave.
Explore: the seven bands: Visiting every band and reading wavelength, frequency, use and risk side by side builds the pattern: shorter waves, higher frequency, more energy, more risk.
Explain: the wave model of light: Transverse waves, the spectrum as one family at one speed, and the link between frequency, wavelength and energy cover the node's first and third success criteria (bending light covers the second); the uses sort connects the pattern to technologies.
Elaborate: choosing a wave: Choosing a band for a job from wavelength, frequency and risk applies the pattern to real communication and medical technologies.
Elaborate: sun safety: Linking the wave model to UV damage explains protective behaviour through the wave property that matters, frequency.
Elaborate: Slip, Slop, Slap: Australia's sun-safety campaigns show why some science is taken up by a whole society: strong evidence, simple low-cost actions, trusted messengers and rules that make the habit normal.
Now you can
Say what makes light and X-rays the same kind of wave.
Say how wavelength, frequency and energy change from radio to gamma.