Teacher's lesson plan · Upper Key Stage 2 (Years 5–6) · 90 minutes, or two 45-minute sessions
Radio waves behave like a light you cannot see. They get weaker the further you go from the source, they are absorbed by solid objects, and they bounce off surfaces. Pupils track a hidden transmitter using a hand-held receiver, and in doing so measure a signal fading with distance and discover that their instrument stops being useful when it is saturated — a problem they solve by deliberately making it less sensitive.
Statements quoted from the national curriculum programmes of study for England (2014).
| Subject | Statutory statement | Where it happens |
|---|---|---|
| Science — working scientifically, upper KS2 | “taking measurements, using a range of scientific equipment, with increasing accuracy and precision, taking repeat readings when appropriate” | Activity 2 |
| Science — working scientifically, upper KS2 | “recording data and results of increasing complexity using scientific diagrams and labels … tables, scatter graphs, bar and line graphs” | Activity 2, plenary |
| Science — working scientifically, upper KS2 | “planning different types of scientific enquiries to answer questions, including recognising and controlling variables where necessary” | Activity 3 |
| Science — working scientifically, upper KS2 | “reporting and presenting findings from enquiries, including conclusions, causal relationships and explanations of and a degree of trust in results” | Plenary |
| Science — Year 6, light | “recognise that light appears to travel in straight lines” | Activity 1, Activity 3 |
| Science — Year 3, light (revisited) | “notice that light is reflected from surfaces”; “recognise that shadows are formed when the light from a light source is blocked by an opaque object” | Activity 3 |
| Science — Year 4, sound (prior learning) | “recognise that sounds get fainter as the distance from the sound source increases” | Starter |
| Maths — Year 6, statistics | “interpret and construct pie charts and line graphs and use these to solve problems” | Activity 2, extension |
| Maths — Year 5, statistics | “solve comparison, sum and difference problems using information presented in a line graph” | Extension |
| Computing — KS2 | “understand computer networks, including the internet; how they can provide multiple services … and the opportunities they offer for communication and collaboration” | Activity 1 discussion |
| Computing — KS2 | “select, use and combine a variety of software … including collecting, analysing, evaluating and presenting data and information” | Activity 2 |
By the end of the lesson, pupils can:
transmitter · receiver · signal strength · absorb · reflect · saturated · attenuate (to make weaker on purpose) · variable · reliable
Radio waves and light are the same kind of thing — electromagnetic waves — differing only in wavelength. The micro:bit transmits at 2.4 GHz, a wavelength of about 12 cm. That is why the whole lesson can lean on what pupils already know about light and sound.
Fading with distance. The signal spreads out over an ever-larger area, so less of it reaches the receiver. Outdoors this project measured −52 dBm at 1 m falling to about −87 dBm at 20 m. Note that it does not fade evenly: most of the drop happens between 3 m and 8 m.
Absorption. A human body is mostly water, which absorbs 2.4 GHz strongly. Standing between the receiver and the transmitter produces a noticeable dip — the basis of Activity 3.
Reflection. Radio waves bounce off the ground, walls and metal fences. Reflected waves can arrive slightly later than the direct wave and partly cancel it. In this project's own field data the signal at 15 m was weaker than at 20 m for exactly this reason. This is a genuine, honest complication — not a mistake — and it is worth showing to pupils rather than hiding.
Direction, and why there is none. The micro:bit's aerial is a track etched into the circuit board, and it is omnidirectional — it receives about equally from every direction. So the Hound genuinely cannot indicate a bearing; it only ever reports strength. The way round this is the pupil's own body: a person is mostly water, which absorbs 2.4 GHz well, so turning on the spot until the reading dips puts the Treasure behind you. Worth being explicit that this is a workaround for a limitation, not a feature of radio.
Directional aerials do exist — a Yagi (the sort once seen on rooftops for television) or a small loop — and competitors in real direction-finding events carry one, which points at the transmitter directly. This activity deliberately does not use one: the built-in aerial is what makes body-shielding necessary, and body-shielding is what makes absorption something pupils feel rather than are told.
Saturation. The display has only 5 bars covering a 35 dB range, so each bar is about 7 dB. Close to the Treasure the signal is stronger than the top of that range, so all 5 bars light and stay lit however much closer you walk. The instrument has run out of room. Pressing button A subtracts 7 dB — exactly one bar — shifting the whole scale so the bars mean something again. Button B resets it. Up to 10 presses are available.
| Time | Activity |
|---|---|
| 10 min | Starter — what do we already know fades? Ask a pupil to speak from across the room, then from the doorway. Draw out Year 4's “sounds get fainter as the distance from the sound source increases”. Repeat the thinking with a torch. Establish the analogy that carries the whole lesson: a radio signal is like a light you cannot see. Ask for predictions: will the signal fade evenly, or fast at first and then slowly? |
| 10 min | Activity 1 — meet the equipment. Show the Treasure: it transmits three separate beacons, loud, medium and quiet, and its display stays dark so it can hide — press a button and it shows its group number for a moment, which is a neat way in to the group idea below. Show the Hound: beeps tell you roughly how close you are (slow, medium, fast alarm), bars show signal strength. Link to computing: this is a small radio network, and the two boards must agree on a group number to talk at all — an address, like a house number. |
| 25 min | Activity 2 — how does the signal fade with distance? Worksheet part 1. Place the Treasure at a marked point. Have every group press button B before they start — a Hound left attenuated from someone's earlier experimenting reads low, and nothing on screen says so. Pupils walk to each marked distance in turn and record the number of lit rows and the beep speed. Insist on repeat readings: the signal wobbles, so take three at each distance and use the middle value — the worksheet asks them to order the three and take the middle, which is the median. Groups plot bars against distance as a line graph. |
| 20 min | Activity 3 — blocking and bouncing. Worksheet part 2. Establish first that the aerial is omnidirectional, so the Hound cannot point anywhere. Then two fair tests, one variable each. (a) Blocking: stand still and turn slowly on the spot, watching the bars. The reading dips when your own body is between the Hound and the Treasure — so the Treasure is behind you. (b) Reflecting: take a reading in the open at 8 m, then at 8 m with a wall close behind you. Discuss why the second reading may be stronger. |
| 15 min | Activity 4 — the problem of a full screen. Worksheet part 3. Send groups to within about 2 m of the Treasure. All 5 bars light. Ask them to step 1 m closer: nothing changes. Pose the problem: how can you find the exact spot if the meter cannot tell 2 m from 1 m? Take suggestions, then introduce button A. Each press makes the Hound 7 dB less sensitive — exactly one bar — so the bars drop and start responding again. Analogy: sunglasses on a bright day, or turning down a radio that is distorting. |
| 5 min | Finish by actually playing. The investigation measures from a Treasure whose position everyone knows, so nobody has hunted anything. Hide it once and let them find it — the worksheet ends by pointing at this, and it is the moment the three tricks stop being exercises. If time is short, do it at the start of the next session with the hunt card. |
| 10 min | Plenary. Worksheet part 4. Share graphs. Was the fade even? Which measurement did pupils trust least, and why? Return to the three objectives. Reveal the project's own field data (extension) and ask why 15 m came out weaker than 20 m. |
Use the hunt card instead of the full worksheet. It is one side of A4 and the goal is simply to find the Treasure. The science is still there but it is carried as tactics rather than taught as content: the three tricks on the card are the three learning objectives, in the order a hunter would meet them.
| Time | Activity |
|---|---|
| 3 min | Hand out cards. Read the three tricks aloud together — that is the whole briefing. Set the boundary and the recall signal. |
| 12 min | Hide the Treasure and let them hunt in pairs or threes. Circulate and ask one question only: “how do you know?” |
| 5 min | Fastest team first: how did they do it? Then the quick think questions on the card. Question 3 is the one to dwell on — pressing A changes the Hound, not the Treasure. |
This works well as a hook before the full lesson, at the end of a topic, or as an outdoor session in its own right. If you run it twice, let the finders hide the Treasure the second time: choosing a hiding place is where they apply what they have noticed about walls and reflections.
| Misconception | How to address it |
|---|---|
| “The signal stops at a certain distance.” | It gets weaker and weaker until the receiver can no longer pick it out. Nothing switches off. The three beacons vanish at different distances precisely because they start at different strengths. |
| “All five bars means I am right on top of it.” | It means at least as strong as the top of the scale. This is the saturation idea, and Activity 4 exists to break it. |
| “Pressing A makes the signal weaker.” | It changes the meter, not the signal. Compare with sunglasses: the sun does not dim. |
| “The reading went up, so I must be closer.” | Not necessarily — a reflection off a wall can raise it. Move and take another reading. |
| “The Hound points at the Treasure.” | It cannot. The aerial is omnidirectional — it receives from every direction about equally — so the reading carries no bearing at all. Blocking the signal with your own body is the only way to recover a direction. Aerials that are directional exist, and real competitors use them; this one is not. |
Part 1. Bars fall as distance increases, but not evenly — readings hold up over the first few metres and then drop away quickly. Expect the display to blank while the sound continues at longer range; the sound is the coarse instrument and the bars the fine one. Readings wobble by about a bar even standing still, which is why repeats matter.
Part 2a. The reading dips when the pupil's body is between Hound and Treasure, because a body absorbs the signal. The dip points away from the Treasure.
Part 2b. Near a wall the reading is often stronger, because a reflected wave arrives as well as the direct one. Some positions may be weaker if the two partly cancel — both answers are correct and both are evidence of reflection.
Part 3. All 5 bars light because the signal is above the top of the meter's range; the meter cannot show “more than maximum”. Pressing A subtracts 7 dB, moving the whole scale so differences show up again. It changes the instrument, not the signal.
Extension. 15 m reads weaker than 20 m because waves reflected off the ground arrive out of step with the direct wave and partly cancel it at that distance. It is a real effect that this project measured and could not explain away — a good moment to discuss trusting data that looks wrong.
If you run this with a class, I would be very grateful to hear how it went — what worked, what did not, what you had to change, and anything the pupils said that surprised you. It is the only way these materials improve.
Steven Murdoch — s.murdoch@ucl.ac.uk