The shape of the lesson
By the end of the lesson, learners can
- What a sensor does: People can check a temperature now and then; a sensor can check it every second, day and night, without mistakes or getting tired.
- Fourteen sensors: For each sensor, know what it measures (the type of data it captures) and a typical use.
- Choosing the right sensor: Exam questions describe a system and ask for the most suitable sensors.
- Sensor: input device that measures a physical quantity.
- ADC: converts analogue readings to digital for the processor.
- Processor: compares readings with stored values and decides; the actuator acts.
- Names: use the syllabus names, e.g. infra-red, moisture, humidity, proximity.
One picture every idea returns to
A sensor is an input device that measures a physical quantity (such as temperature, light or pressure) in its surroundings and sends the reading to a processor. Most sensors produce an analogue signal, which an analogue-to-digital converter (ADC) turns into digital data. Sensors are used in monitoring systems (record and warn) and control systems (the processor compares readings with stored values and makes an actuator act). Sensors only measure: they never make decisions or act on their own.
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, Measuring the world.. A sensor lets a computer notice what is happening around it: how hot, how bright, how wet or how close. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: What a sensor does | People can check a temperature now and then; a sensor can check it every second, day and night, without mistakes or getting tired. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Fourteen sensors | For each sensor, know what it measures (the type of data it captures) and a typical use. | Pairs |
| 21 to 30 min | Teach and check: Choosing the right sensor | Exam questions describe a system and ask for the most suitable sensors. Model the worked example Automatic greenhouse on the board, one line at a time. Your turn: Which sensor would a car use to warn the driver it is about to reverse into a wall? | Frayer Model |
| 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 (6 questions, 16 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 Choosing the right sensor, 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.
Frayer Model
Pairs fill a four-box grid for the key term: definition, characteristics, examples and non-examples. The non-examples box is where the misconceptions surface, so give it the most time.
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 |
|---|---|
| Never write "the sensor turns on the heater" or "the sensor decides". | The sensor only sends readings; the microprocessor compares and decides; the actuator acts. |
| Moisture and humidity are different. | Moisture is water in the soil (or a material); humidity is water vapour in the air. |
| Answer with sensor names from the syllabus list. "Motion sensor" or "heat sensor" may not earn the mark: say infra-red or temperature. | Return to Choosing the right sensor: ask a pair to state the correct version and show it on the lab before moving on. |
Sensors and how they are used: worksheet
6 questions, 16 marks. Written in the style of the papers; no past paper question is reproduced.
State what is meant by a sensor and give one reason why sensors are used instead of a person taking readings.
Identify the most suitable sensor for each use.
(a) Detecting a burglar stepping on a mat.
(b) Measuring the amount of fuel left in a tank.
(c) Measuring how fast water moves through a pipe.
An art gallery must keep its paintings in air that is not too warm, not too damp and not too bright. Identify three sensors it should use.
A greenhouse uses a moisture sensor to keep the soil watered. Explain how the sensor and microprocessor keep the soil at the correct moisture level.
Explain the difference between a moisture sensor and a humidity sensor.
A student writes: "The temperature sensor switches the heater on when it gets cold." Explain why this is incorrect.
Answer key and marking notes
- An input device that measures a physical quantity / captures data about its environment.
- Any one: readings are taken continuously/more often; more accurate; can be used in dangerous or remote places; no need for a person to be present.
- (a) Pressure sensor.
- (b) Level sensor.
- (c) Flow sensor.
- Temperature sensor.
- Humidity sensor.
- Light sensor.
- The moisture sensor measures the water content of the soil and sends the reading (via an ADC) to the microprocessor.
- The microprocessor compares the reading with a stored value.
- If the reading is below the stored value, it sends a signal to an actuator to open the water valve / switch on the sprinkler; otherwise it closes it.
- The process repeats continuously.
- A moisture sensor measures the water content of soil (or a material).
- A humidity sensor measures the amount of water vapour in the air.
- The sensor only measures the temperature and sends the reading.
- The microprocessor compares the reading with the stored value and sends the signal that switches the heater on.
6 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.
What does a humidity sensor measure?
- Athe amount of water vapour in the air
- Bthe water content of the soil
- Chow high a liquid is in a container
- Dthe acidity or alkalinity of water
A garden system waters plants automatically when the soil becomes too dry. Which sensor is needed?
- Amoisture
- Bhumidity
- Clevel
- Dflow
A car warns the driver when it is about to reverse into a wall. Which sensor is most suitable?
- Aproximity
- Bpressure
- Caccelerometer
- Dmagnetic field
In a central heating control system, which statement is correct?
- AThe microprocessor compares the temperature reading with a stored value and signals the heater if needed
- BThe temperature sensor compares the reading with the stored value and turns the heater on
- CThe heater measures the temperature and tells the microprocessor when to switch off
- DThe temperature sensor sends readings only when the user presses a button
Why does a temperature sensor usually need an analogue-to-digital converter (ADC) before its readings reach the microprocessor?
- ATemperature varies smoothly so the sensor gives an analogue signal, but the microprocessor only processes digital data
- BThe microprocessor produces analogue data that the sensor cannot understand
- CThe ADC makes the readings more accurate by adding extra decimal places
- DThe ADC stores the readings so that the microprocessor can collect them later
A leisure centre wants to monitor its swimming pool so that the water stays safe and comfortable. Which pair of sensors is most suitable?
- ApH and temperature
- Bhumidity and light
- Cmoisture and acoustic
- Dproximity and flow
Quiz key
A humidity sensor measures water vapour in the air, for example in a greenhouse or a museum. Water content of soil is measured by a moisture sensor, the height of a liquid by a level sensor, and acidity or alkalinity by a pH sensor.
A moisture sensor measures the water content of the soil, which is exactly what decides when to water. Humidity is water vapour in the air, a level sensor measures how full a container is, and a flow sensor measures how fast a liquid moves through a pipe.
A proximity sensor measures how close an object is without touching it, so it can warn before a collision. A pressure sensor would only respond once something pressed on it, an accelerometer measures movement and acceleration (used for airbags after a crash), and a magnetic field sensor detects changes in a magnetic field, which a wall does not produce.
The sensor only measures and sends readings; the microprocessor compares each reading with the stored value and decides; the actuator (the heater's switch) acts. A sensor never decides or switches anything on, and the heater does not measure. Sensors send readings continuously, in a loop, not only when a button is pressed.
Physical quantities such as temperature vary continuously, so most sensors output an analogue signal; the microprocessor can only process binary, so the ADC converts the signal to digital. The microprocessor works in digital, not analogue. Converting cannot add real accuracy, and an ADC converts rather than stores readings.
Pool water must have the right acidity (measured by a pH sensor) and the right warmth (measured by a temperature sensor). Humidity is water vapour in the air and light measures brightness, neither of which is the water's condition. Moisture is for soil and acoustic sensors measure sound. Proximity measures how close an object is; flow could check the pumps but proximity tells nothing about the water.
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.