Choosing the most suitable sensor for a given context

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Quick Questions

Shade in the A or B circle for each question.

1. A street lamp must switch on automatically when it gets dark. Which sensor is most suitable?

A Pressure sensor, because it measures how bright the surroundings are

B Light sensor, because it measures how bright the surroundings are

2. A burglar alarm must detect someone moving in a dark room at night. Which sensor is most suitable?

A Infra-red sensor, because it detects the heat given off by a moving person

B pH sensor, because it detects the heat given off by a moving person

3. A greenhouse computer must keep the air warm enough for tomato plants. Which sensor should it use?

A Magnetic field sensor, because the system needs to measure how hot the air is

B Temperature sensor, because the system needs to measure how hot the air is

4. A greenhouse must water plants only when the soil is dry. Which sensor is most suitable?

A Moisture sensor, because it measures how much water is in the soil

B Acoustic sensor, because it measures how much water is in the soil

5. A water tank must stop filling when it is full. Which sensor is most suitable?

A Level sensor, because it measures how high the water has risen in the tank

B Light sensor, because it measures how high the water has risen in the tank

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1Street lamps switch on at dusk: light sensor		AThe system must measure how wet the soil is, so a moisture sensor is the suitable choice
2Greenhouse watering: moisture sensor		BThe sensor does not measure the needed quantity. A car park needs to detect the presence or weight of a car, not temperature, and 'measures cars' is not a real reason.
3For a burglar alarm that detects someone moving into a room, find the quantity (movement) and choose the sensor that measures it		CUse an infra-red sensor because it detects body heat and movement of an intruder
4For a water tank that must not overflow, find the quantity (height of the water) and choose the sensor that measures it		DThe system must measure brightness, so a light sensor is the suitable choice
5Use a temperature sensor to detect a car in a parking space, because it measures cars		EUse a level sensor because it measures how high the water is in the tank
6Use a sensor in the greenhouse because it is a good sensor		FNo sensor is named and no physical quantity is identified, so the justification is vague and gets no marks.

Definitions

suitable sensor

Fill in the Blanks

Complete each line of code by filling in the missing parts.

Context: burglar alarm Quantity to measure: heat from a person Sensor: _________

Context: greenhouse soil needs watering Sensor: ________ Because it measures water in the soil

Context: street lamps switch on at night Sensor: _____ Because it measures how bright it is

Context: water tank must not overflow Sensor: level sensor Suitable _______ it measures water height

Context: car park shows if a bay is taken Quantity to measure: weight of the car Sensor: ________

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A sensor ← infra-red

B IF motion = TRUE THEN

C alarm ← OFF

D ENDIF

Question 2

A // Water greenhouse plants

B sensor ← pH

C IF reading < 30 THEN

D sprinkler ← ON

E ENDIF

Question 3

A REPEAT

B level ← light sensor

C IF level > 20 THEN

D lamp ← ON

E UNTIL FALSE

Question 4

A sensor ← level

B READ height FROM sensor

C IF height >= 90 THEN

D pump ← ON

E ENDIF

Question 5

A FOR each bay

B sensor ← humidity

C IF reading > 0 THEN

D bay ← FULL

E NEXT

Answer Key

Choosing the most suitable sensor for a given context

Section A: Quick Questions

B — Light sensor, because it measures how bright the surroundings are

A — Infra-red sensor, because it detects the heat given off by a moving person

B — Temperature sensor, because the system needs to measure how hot the air is

A — Moisture sensor, because it measures how much water is in the soil

A — Level sensor, because it measures how high the water has risen in the tank

Section B: Match the Pairs

Street lamps switch on at dusk: light sensor → The system must measure brightness, so a light sensor is the suitable choice

Greenhouse watering: moisture sensor → The system must measure how wet the soil is, so a moisture sensor is the suitable choice

For a burglar alarm that detects someone moving into a room, find the quantity (movement) and choose the sensor that measures it → Use an infra-red sensor because it detects body heat and movement of an intruder

For a water tank that must not overflow, find the quantity (height of the water) and choose the sensor that measures it → Use a level sensor because it measures how high the water is in the tank

Use a temperature sensor to detect a car in a parking space, because it measures cars → The sensor does not measure the needed quantity. A car park needs to detect the presence or weight of a car, not temperature, and 'measures cars' is not a real reason.

Use a sensor in the greenhouse because it is a good sensor → No sensor is named and no physical quantity is identified, so the justification is vague and gets no marks.

Section C: Definitions

suitable sensor — The sensor that measures the physical quantity a system needs, e.g. light for street lamps or pressure for a car park. Justify it with 'because'.

Section D: Fill in the Blanks

Context: burglar alarm
Quantity to measure: heat from a person
Sensor: infra-red

Context: greenhouse soil needs watering
Sensor: moisture
Because it measures water in the soil

Context: street lamps switch on at night
Sensor: light
Because it measures how bright it is

Context: water tank must not overflow
Sensor: level sensor
Suitable because it measures water height

Context: car park shows if a bay is taken
Quantity to measure: weight of the car
Sensor: pressure

Section E: Spot the Error

C — When the infra-red sensor detects movement in a burglar alarm system, the alarm actuator must be switched ON, not OFF. The line should be: alarm ← ON.

B — Watering depends on how dry the soil is, so the physical quantity is moisture. A moisture sensor is the suitable sensor; a pH sensor measures acidity, not dryness. It should be: sensor ← moisture.

C — Street lamps should come on when it is dark, which means a LOW light reading. The condition should be level < 20, otherwise the lamps would switch on in daylight.

D — A level sensor shows the water tank is nearly full at 90 or more, so the pump must be switched OFF to stop it overflowing. It should be: pump ← OFF.

B — A car in a parking bay presses on the ground with its weight, so the quantity to measure is pressure. A humidity sensor measures moisture in the air and cannot detect a car. It should be: sensor ← pressure.