IGCSE Computer Science: Input and Output Devices — Practice Questions (Cambridge 0478)

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — Cambridge International holds copyright in its own papers. Use these alongside the official past papers available free from your board.

Related: Hardware study guide and revision notes

Input and output devices are syllabus section 3.2 of Cambridge IGCSE Computer Science (0478), syllabus for 2026, 2027 and 2028, in Topic 3 Hardware. You must understand what an input device and an output device are and why each is needed, know how each listed device works and where it is used, and choose the most suitable sensor for a given situation. The section is examined on Paper 1 Computer Systems (1 hour 45 minutes, 75 marks). These questions cover all three learning outcomes; the answers show what earns each mark. For questions on the CPU, storage and network hardware, use the Hardware practice questions.

What does syllabus section 3.2 cover?

Outcome	Content
3.2 (1)	Input devices and why they are needed: barcode scanner, digital camera, keyboard, microphone, optical mouse, QR code scanner, touch screens (resistive, capacitive, infra-red), 2D and 3D scanners
3.2 (2)	Output devices and why they are needed: actuator, DLP projector, inkjet printer, laser printer, LED screen, LCD projector, LCD screen, speaker, 3D printer
3.2 (3)(a)-(b)	Sensors and their purpose (acoustic, accelerometer, flow, gas, humidity, infra-red, level, light, magnetic field, moisture, pH, pressure, proximity, temperature); the type of data each captures; selecting the most suitable sensor

Questions

1. State what is meant by an input device and why a computer needs one. [2]

2. A supermarket uses barcode scanners at its checkouts.

(a) Describe how a barcode scanner reads a barcode. [4] (b) The supermarket also prints QR codes on its posters. Give two differences between a QR code and a barcode. [2]

3. A museum wants a touch screen information point in its entrance hall. Visitors will often be wearing gloves in winter.

(a) Explain why a capacitive touch screen would not be suitable. [2] (b) Identify a suitable type of touch screen and describe how it detects a touch. [3]

4. Describe how an optical mouse detects movement. [3]

5. Explain how a 3D scanner captures an object, and give one use. [3]

6. A school prints 2 000 copies of a black-and-white newsletter every week. A teacher prints a few colour photos at home.

(a) Identify the most suitable type of printer for each, giving a reason. [4] (b) Describe how a laser printer produces a printed page. [4]

7. Describe how a 3D printer produces a solid object. [3]

8. Compare an LCD screen and an LED screen. [3]

9. A conference room uses a DLP projector. Describe how a DLP projector creates an image. [3]

10. State what is meant by an actuator and give one example of its use in a control system. [2]

11. Identify the most suitable sensor for each situation.

Situation	Sensor
(a) Detecting whether a car is parked in a car park space
(b) Checking the acidity of water in a fish tank
(c) Detecting when a smartphone is rotated
(d) Warning of a carbon monoxide leak in a kitchen
(e) Monitoring how fast water moves through a pipe
(f) Deciding when to switch on street lights

[6]

12. An automatic greenhouse watering system uses a sensor and a microprocessor.

(a) Identify the most suitable sensor and the type of data it captures. [2] (b) Explain how the system keeps the soil at the right level of moisture. [4]

13. Explain why the readings from a temperature sensor must be converted before a computer can process them. [2]

Answers

1. A device that allows data to be entered into a computer [1] so that it can be processed / the user can communicate instructions to the computer [1].

2. (a) Any four [1 each]: the barcode is lit with a red light / laser; black bars reflect less light and white spaces reflect more; sensors detect the reflected light; the pattern is converted into a digital (binary) value / number; the number is looked up in a database to find the product details. (b) Any two [1 each]: a QR code is two-dimensional, a barcode is one-dimensional; a QR code can store much more data (such as a web address); a QR code can be read by a smartphone camera; a QR code can be read from any angle.

3. (a) A capacitive screen detects a change in the electrical charge (field) on the screen when a conductive finger touches it [1]; gloves do not conduct, so no change is detected [1]. (b) An infra-red touch screen [1] (accept resistive with a valid description). Infra-red beams are sent across the screen in a grid from LEDs to sensors on the edges [1]; a touch blocks beams, and the position is worked out from which beams are broken [1]. Resistive alternative: two conductive layers are pressed together by the touch [1], completing a circuit, and the point of contact is calculated [1].

4. An LED shines light onto the surface beneath the mouse [1]; a sensor (camera) takes many images per second of the reflected light [1]; changes between images are processed to calculate the direction and distance moved [1].

5. Lasers / light are directed at the object from many angles and the reflections are measured by sensors [1]; the measurements are used to build a 3D digital model [1]. Use [1]: for example to make a model for 3D printing, or in medical scanning or reverse engineering.

6. (a) Newsletter: laser printer [1], because it is fast and economical for large volumes of high-quality text [1]. Photos: inkjet printer [1], because it gives good-quality colour output and is cheap to buy for small numbers of prints [1]. (b) Any four [1 each]: the rotating drum is given an electrostatic charge; a laser beam scans across the drum and changes the charge in places, creating an electrostatic image of the page; charged toner is attracted only to the parts of the drum that form the image; the paper is charged so the toner transfers from the drum to the paper; a fuser uses heat (and pressure) to fix the toner onto the paper; the charge on the drum is removed ready for the next page.

7. A digital design is produced (for example by CAD or a 3D scanner) [1]; the design is sliced into layers [1]; the printer builds the object layer by layer, for example by extruding melted plastic that hardens [1].

8. Both are flat-panel screens made of pixels [1]. An LCD screen uses liquid crystals that change to let light through or block it, and needs a separate backlight [1]. An LED screen uses LEDs (for the backlight or as the pixels), which uses less power / gives brighter images / a thinner screen [1].

9. Light from a bright lamp passes through a colour wheel / filter [1] onto millions of tiny mirrors (a digital micromirror device), one per pixel [1]; each mirror tilts towards or away from the lens to make that pixel light or dark, projecting the image [1].

10. An output device that converts an electrical signal into physical movement [1]; for example a motor that opens a window in a greenhouse, or a valve that turns on a heating system [1].

11. [1 each] (a) proximity (or magnetic field / infra-red); (b) pH; (c) accelerometer; (d) gas; (e) flow; (f) light.

12. (a) Moisture sensor [1]; it captures the amount of water in the soil (as an analogue value) [1]. (b) The sensor sends readings to the microprocessor (via an ADC) [1]; the microprocessor compares each reading with a preset value [1]; if the soil is too dry, it sends a signal to an actuator to open a valve / switch on a pump [1]; when the reading reaches the preset value it closes the valve; readings are taken continuously in a loop [1].

13. A sensor produces analogue data / a continuously varying signal [1]; a computer can only process digital (binary) data, so an analogue-to-digital converter is needed [1].

Where marks are usually lost

• Saying a capacitive screen detects “pressure” (that is a resistive screen).
• Giving a sensor that does not measure what the situation needs, such as a temperature sensor to detect a parked car.
• Describing a laser printer without the charged drum and toner.
• Forgetting that the microprocessor compares the reading with a preset value.
• Confusing an actuator (output) with a sensor (input).

Frequently asked questions

Is a touch screen an input or an output device? It is both: the display is output, and the touch-sensitive layer is input. The syllabus lists touch screens as input devices because the exam focuses on how they detect touch.

Does a sensor make decisions? No. A sensor only measures and sends data. The microprocessor compares the data with preset values and decides whether to signal an actuator.

Do I need to know how a microphone and speaker work? Yes, in outline. A microphone converts sound vibrations into an electrical signal; a speaker converts an electrical signal into vibrations of a cone, producing sound.

Official syllabus

Cambridge IGCSE Computer Science (0478) syllabus for examination in 2026, 2027 and 2028, Topic 3 Hardware, section 3.2 Input and output devices, published by Cambridge International Education.