O Level Computer Science: Input and Output Devices — Practice Questions (Cambridge 2210)

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 O Level Computer Science (2210), syllabus for 2026, 2027 and 2028, in Topic 3 Hardware. You need to explain what input and output devices are and why they are needed, describe how each device on the syllabus list works and where it is used, and pick the best sensor for a given context. The section is examined on Paper 1 Computer Systems. The questions below are built around everyday scenarios and cover every listed device; for the CPU, storage and networking, see 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 (acoustic, accelerometer, flow, gas, humidity, infra-red, level, light, magnetic field, moisture, pH, pressure, proximity, temperature): their purpose, the data each captures, and choosing the most suitable one

Questions

1. State what is meant by an output device and why it is needed. [2]

2. A student types an essay on a keyboard. Describe how a keyboard sends a key press to the computer. [3]

3. A digital camera is used to photograph a school event.

(a) Describe how a digital camera captures an image. [3] (b) Explain one reason why the photographer might choose a higher resolution setting, and one drawback. [2]

4. A library scans old printed documents so they can be stored on a computer.

(a) Describe how a 2D scanner captures a page. [3] (b) The library wants to search the text in the scans. Identify the software needed. [1]

5. A restaurant shows a QR code on each table. Customers scan it with a smartphone to see the menu.

(a) Describe how the smartphone reads the QR code. [3] (b) Give one benefit to the restaurant of using QR codes. [1]

6. A cash machine (ATM) uses a resistive touch screen.

(a) Describe how a resistive touch screen detects a touch. [3] (b) Give one advantage and one disadvantage of a resistive screen compared with a capacitive screen. [2]

7. A voice assistant uses a microphone and a speaker.

(a) Describe how a microphone converts sound into data. [3] (b) Describe how a speaker produces sound from digital data. [3]

8. A school hall uses an LCD projector. Describe how an LCD projector produces an image. [3]

9. An office printer has run out of ink. The office manager is choosing between an inkjet and a laser printer. Explain two reasons why a laser printer might be the better choice for the office. [4]

10. Describe how an inkjet printer produces a printed page. [4]

11. An engineering company uses a 3D printer to make prototype parts. Give two benefits of this. [2]

12. A smart home has a heating system controlled by a microprocessor.

(a) Identify the sensor used and the actuator that changes the room temperature. [2] (b) Explain how the system keeps the room at the temperature set by the user. [4]

13. Identify the most suitable sensor for each use, and the type of data it captures.

(a) A burglar alarm that detects a person moving in a dark room. [2] (b) A system that warns when the water in a tank is about to overflow. [2] (c) A machine that measures how damp the air is in a museum display case. [2] (d) A device that detects breaking glass by its sound. [2]

Answers

1. A device that shows or produces the results of processing in a form the user (or another device) can use [1], so that information can be communicated out of the computer, for example as a display, printout, sound or movement [1].

2. Pressing a key completes a circuit under the key [1]; the keyboard’s processor works out which key was pressed [1] and sends its character code (for example in ASCII or Unicode) to the computer [1].

3. (a) Light passes through the lens onto an image sensor (made of millions of light-sensitive cells) [1]; each cell measures the light falling on it to make one pixel [1]; the values are converted into binary and stored as an image file on the memory card [1]. (b) Benefit: more pixels give more detail, so images can be enlarged or cropped without looking blocky [1]. Drawback: larger file sizes take up more storage / take longer to transfer [1].

4. (a) A bright light moves across the page [1]; light reflected from the page is captured by sensors (for example via mirrors and a lens) [1]; the readings are converted into digital data to form an image of the page [1]. (b) Optical character recognition (OCR) software [1].

5. (a) The camera captures an image of the QR code [1]; software identifies the three position squares to orient it [1]; the pattern of black and white squares is decoded into data, such as the web address of the menu [1]. (b) Any one [1]: menus can be updated without reprinting; fewer printed menus to clean or replace; it can link customers straight to ordering online.

6. (a) The screen has two flexible conductive layers separated by a small gap [1]; pressing the screen pushes the layers together, completing a circuit [1]; the point of contact is calculated from where the layers touched [1]. (b) Advantage [1]: it works with gloves or a stylus / is cheaper / is not affected by water. Disadvantage [1]: it is less responsive and less clear / does not support multi-touch / the top layer can be scratched.

7. (a) Sound waves make a diaphragm vibrate [1]; the vibrations move a coil in a magnetic field (or change a capacitance), producing an electrical (analogue) signal [1]; the signal is converted to digital data by an analogue-to-digital converter (ADC) [1]. (b) Digital data is converted to an analogue electrical signal by a digital-to-analogue converter (DAC) [1]; the varying current passes through a coil, creating a changing magnetic field that moves the coil and cone in and out [1]; the cone makes the air vibrate, producing sound waves [1].

8. A bright light from a lamp is split into red, green and blue beams [1]; each beam passes through an LCD panel whose pixels let light through or block it to form that colour’s version of the image [1]; the three images are combined and projected through a lens onto the screen [1].

9. Any two developed reasons [2 each]: it prints much faster [1], so large numbers of pages are produced quickly [1]; toner cartridges print many more pages than ink cartridges [1], so the cost per page is lower for high volumes [1]; the output is sharp text that does not smudge [1], which suits office documents [1]; it has a larger paper tray [1], so it needs refilling less often [1].

10. Any four [1 each]: data from the document is sent to the printer and stored in a buffer; the paper is fed in and moved one line at a time; the print head moves across the page; tiny droplets of ink are fired through nozzles onto the paper (using thermal bubble or piezoelectric technology); the paper advances and the process repeats until the page is complete.

11. Any two [1 each]: a prototype can be made quickly from a digital design; complex shapes can be produced in one piece; designs can be changed and reprinted cheaply; less material is wasted.

12. (a) Temperature sensor [1]; actuator such as a heater switch / valve on the radiator / boiler control [1]. (b) The temperature sensor sends readings to the microprocessor (via an ADC) [1]; the microprocessor compares the reading with the temperature set by the user [1]; if it is lower, it sends a signal to the actuator to switch the heating on, and if it is higher, to switch it off [1]; this repeats continuously [1].

13. [1 for sensor, 1 for data, each part] (a) Infra-red sensor (accept proximity); detects heat (infra-red radiation) given off by a person / a broken infra-red beam. (b) Level sensor; measures the height (level) of the water in the tank. (c) Humidity sensor; measures the amount of water vapour in the air. (d) Acoustic sensor; measures sound (sound level / frequency).

Where marks are usually lost

• Describing a resistive screen as detecting electrical charge from the finger (that is capacitive).
• Forgetting the ADC when a sensor or microphone sends data to a computer, or the DAC for a speaker.
• Choosing a moisture sensor when the question is about air (that needs a humidity sensor).
• Giving “faster” as a reason with no consequence in a two-mark explain question.
• Mixing up LCD and DLP projectors.

Frequently asked questions

What is the difference between a moisture sensor and a humidity sensor? A moisture sensor measures water in a material such as soil. A humidity sensor measures water vapour in the air.

Why is an actuator an output device? It receives a signal from the computer and turns it into physical movement, such as opening a valve or turning a motor.

Do I need to name the parts of a laser or inkjet printer? You should describe the main stages and parts in order: for an inkjet, the print head and nozzles; for a laser printer, the charged drum, laser, toner and fuser.

Official syllabus

Cambridge O Level Computer Science (2210) syllabus for examination in 2026, 2027 and 2028, Topic 3 Hardware, section 3.2 Input and output devices, published by Cambridge International Education.