← IGCSE Computer Science Paper 1

What a sensor is

An input device that measures a physical quantity, such as heat or light, from the environment and sends the readings to a computer or microprocessor.

Part of: IGCSE Computer Science 0478 — 3.2 Input and Output Devices — Module 32, IGCSE Computer Science 0478 — 6.1 Automated Systems — Module 2, IGCSE Computer Science 0478 — 6.2 Robotics — Module 4, ACARA Digital Technologies Years 7–8 — Acquiring and Storing Data — Module 14, ACARA Digital Technologies Years 9–10 — Acquiring and Validating Data — Module 26, QCE Digital Solutions Unit 2 — Data and Programming Techniques — Module 14, QCE Digital Solutions Unit 3 — Interactions Between Users, Data and Digital Systems — Module 75

Understanding What a sensor is in IGCSE Computer Science Paper 1

What it does: The sensor sends data in to the computer, which is what an input device does. The loop keeps taking readings over and over, so the system can monitor automatically without a person. Sensors measure physical quantities such as temperature, light or pressure. A password is data typed in by a person, not something in the environment. This is the definition of a sensor: it measures the environment and passes the readings to a processor.

Common mistakes: A temperature reading must come from a sensor, which is an input device. An actuator is an output device that carries out an action. It should be tempSensor(). When the sensor reading shows it is too hot (above 30), the system should switch the fan ON to cool the room. It should be fan ← ON.

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This module's key terms are also in a printable crossword (Modules 273–282) and word search (Modules 262–282).

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Learning
Duo
Which statement describes a sensor correctly?
An input device that measures a physical quantity and sends readings to a computerAn output device that displays results to the user
Matches
A sensor is an output device that shows data to the user.
↓
A sensor is an input device, not an output device. It measures the environment and sends readings in to the computer.
Applying
Meanings
Term
sensor
Meaning
An input device that measures a physical quantity, such as heat or light, from the environment and sends the readings to a computer or microprocessor.
Practice
WHILE TRUE
Testing
Gaps
TRUE DO
Check Answer
Spots
1WHILE TRUE
2 reading ← tempActuator()

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Quick Questions

1. Which statement describes a sensor correctly?
A. An input device that measures a physical quantity and sends readings to a computer ✓
B. An output device that displays results to the user
A sensor is an input device. It measures something in the environment and sends the readings to a computer or microprocessor.
2. Which of these is a physical quantity that a sensor can measure?
A. Temperature ✓
B. Password
Sensors measure physical quantities such as temperature, light or pressure. A password is data typed in by a person, not something in the environment.
3. Where do sensor readings go after they are measured?
A. To a computer or microprocessor ✓
B. Straight to the keyboard
Sensors send their readings to a computer or microprocessor, which processes the data.
4. True or false: A sensor is an input device.
A. False
B. True ✓
Sensors send data into the computer system, so they are input devices.
5. How do sensors usually take readings?
A. Only when a person presses a key
B. Continuously, again and again ✓
Sensors keep measuring the environment, so the system always has up-to-date readings. They do not need a person to trigger each reading.

Match the Pairs

sensor → An input device that measures a physical quantity, such as heat or light, from the environment and sends the readings to a computer or microprocessor.
temperature = read_sensor() → The computer takes a reading of a physical quantity (heat) that a sensor has measured and stores it in a variable.
A sensor is an input device, so its readings go into the computer for processing. → INPUT reading FROM sensor
Sensors take continuous readings so a system can monitor and control without a person. → WHILE TRUE reading ← sensor value ENDWHILE
A sensor is an output device that shows data to the user. → A sensor is an input device, not an output device. It measures the environment and sends readings in to the computer.
A light sensor measures the sound level in a room. → A light sensor measures light, not sound. Sound is measured by an acoustic sensor.

Key Term

sensor
An input device that measures a physical quantity, such as heat or light, from the environment and sends the readings to a computer or microprocessor.

Fill in the Blanks

1. WHILE TRUE DO temp ← READ(tempSensor) ENDWHILE
Hint: Type the loop keyword that keeps taking sensor readings over and over.
2. WHILE TRUE DO light ← READ(lightSensor) ENDWHILE
Hint: Type the function name that gets the latest reading from the sensor.
3. IF temp > 30 THEN OUTPUT "Fan on" ENDIF
Hint: Type the comparison operator meaning 'greater than'.
4. reading ← READ(tempSensor) OUTPUT reading
Hint: Type the variable name that stores the value the sensor sent to the computer.
5. IF temp < 18 THEN heater ← ON ENDIF
Hint: Type the state that makes the heater work automatically when it is too cold.

Spot the Error

Question 1
A WHILE TRUE
B reading ← tempActuator()
C OUTPUT reading
D ENDWHILE
Line B — A temperature reading must come from a sensor, which is an input device. An actuator is an output device that carries out an action. It should be tempSensor().
Question 2
A WHILE TRUE
B temp ← tempSensor()
C IF temp > 30 THEN
D fan ← OFF
E ENDIF
F ENDWHILE
Line D — When the sensor reading shows it is too hot (above 30), the system should switch the fan ON to cool the room. It should be fan ← ON.
Question 3
A // Sensors are output devices
B temp ← tempSensor()
C OUTPUT temp
Line A — A sensor sends data into the computer, so it is an input device, not an output device. The comment should say input devices.
Question 4
A DECLARE temp : REAL
B temp ← lightSensor()
C OUTPUT temp
Line B — The variable temp stores heat, so it needs a temperature sensor. A light sensor measures light, not heat. It should be tempSensor().
Question 5
A reading ← pressureSensor()
B // sent to the microprocessor
C IF alarm > 100 THEN
D alarm ← ON
E ENDIF
Line C — The microprocessor must check the sensor reading, not the alarm. The condition should test reading: IF reading > 100 THEN.

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