The shape of the lesson
By the end of the lesson, learners can
- Sweep across the spectrum: Move along the bands from radio to gamma and watch the wavelength shorten and the frequency climb.
- Seven bands, one speed: The regions differ in wavelength and frequency, but in a vacuum they all travel at the same speed.
- Order: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma (longest to shortest wavelength).
- Speed: all EM waves travel at 3.0 x 10^8 m/s in a vacuum. Only wavelength and frequency change.
- Equation: v = f x wavelength, so wavelength = v / f.
One picture every idea returns to
All electromagnetic waves are transverse and travel at 3 x 10⁸ m/s in a vacuum. From radio waves to gamma rays the wavelength gets shorter and the frequency higher. Visible light is only a thin band in the middle.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, One family, many wavelengths.. Radio waves, the light you see, and the gamma rays from space are all the same kind of wave, differing only in wavelength. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Sweep across the spectrum | Move along the bands from radio to gamma and watch the wavelength shorten and the frequency climb. Project tab 1 of the lab (Regions and uses) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Seven bands, one speed | The regions differ in wavelength and frequency, but in a vacuum they all travel at the same speed. Model the worked example Worked example on the board, one line at a time. | Cooperative Concept Mapping |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (7 questions, 18 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Seven bands, one speed, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Cooperative Concept Mapping
Teams receive the key terms on cards and arrange them on a large sheet, drawing and labelling the links. Compare maps between teams before showing the model map.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Every electromagnetic wave travels at the same speed in a vacuum, whatever its frequency. | What changes across the spectrum is the wavelength and frequency, not the speed. Visible light is only a thin slice sitting between infrared and ultraviolet. |
The electromagnetic spectrum: worksheet
7 questions, 18 marks. Written in the style of the papers; no past paper question is reproduced.
List the seven regions of the electromagnetic spectrum in order, starting with the region that has the longest wavelength.
State two properties that all electromagnetic waves have in common.
A mobile phone communicates using microwaves of wavelength 0.15 m. Calculate the frequency of these microwaves. (speed of EM waves = 3.0 x 10^8 m/s)
State a typical use for each of the following regions of the electromagnetic spectrum:
(a) radio waves, [1] (b) infrared, [1] (c) ultraviolet, [1] (d) gamma rays. [1]Of all the regions of the electromagnetic spectrum, state which has:
(a) the highest frequency, [1] (b) the longest wavelength. [1]A student says that because gamma rays carry far more energy than radio waves, they must travel much faster. Explain why this is wrong.
Identify the region of the electromagnetic spectrum used in each case, and you do not need to explain.
(a) Sending a television picture from a satellite to a home dish. [1] (b) Taking an image of a broken bone in a hospital. [1] (c) Changing channels with a television remote control. [1]Answer key and marking notes
Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. ✓✓
This is also the order of increasing frequency. Longest wavelength means lowest frequency.
- They are all transverse waves. ✓
- They all travel at the same speed in a vacuum, 3.0 x 10^8 m/s. ✓
Rearrange: v = f x wavelength, so f = v / wavelength
f = (3.0 x 10^8) / 0.15f = 2.0 x 10^9 Hz
That is 2.0 GHz, a typical mobile phone frequency. The answer is sensible.
(a) Television or radio broadcasting. ✓
(b) Remote controllers, intruder alarms, or thermal imaging. ✓
(c) Security marking, sterilising water, or detecting forged banknotes. ✓
(d) Sterilising equipment and food, or treating cancer. ✓
(a) Gamma rays. ✓
(b) Radio waves. ✓
Highest frequency and shortest wavelength go together (gamma). Lowest frequency and longest wavelength go together (radio).
- All electromagnetic waves travel at the same speed in a vacuum, 3.0 x 10^8 m/s, regardless of their energy. ✓
- Gamma rays differ from radio waves by having a much shorter wavelength and higher frequency, not a higher speed. ✓
(a) Microwaves. ✓
(b) X-rays. ✓
(c) Infrared. ✓
Satellite and mobile signals, microwaves. Bones and airport scanners, X-rays. Remotes and alarms, infrared.
3 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
The diagram shows the electromagnetic spectrum. Which region has the longest wavelength?
- Aradio waves
- Bultraviolet
- CX-rays
- Dgamma rays
In a vacuum, how do the speeds of radio waves and gamma rays compare?
- AThey travel at the same speed, about 3 × 108 m/s.
- BRadio waves travel faster.
- CGamma rays travel faster.
- DRadio waves do not travel through a vacuum.
Which region of the electromagnetic spectrum is used by a television remote control?
- Ainfrared
- Bgamma rays
- CX-rays
- Dvisible light
Quiz key
Radio waves have the longest wavelength of the electromagnetic spectrum. Gamma rays sit at the opposite end with the shortest wavelength and the highest frequency.
All electromagnetic waves travel at the same speed in a vacuum, about 3 × 108 m/s. They differ in frequency and wavelength, not in speed through a vacuum.
A remote control sends infrared signals to the television. Gamma rays and X-rays are far too high in energy and are not used for this everyday purpose.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.