References only, not question text. Open Official paper ↗ where Cambridge publishes the paper,
or see the official Cambridge past-papers page; for other papers, ask your
school. “Paper 42” means Paper 4, variant 2.
Practice questions
Original questions written by HomiLabs in the style of the exam, with answers and mark schemes. They are not
Cambridge past paper questions and have not been reviewed by Cambridge. Try each one before opening the answer.
Q1Logic gates & circuits · Core · Paper 1 style · 3 marks
(a)Complete the truth table for the logic expression X = (A AND B) OR (NOT C). List the output X for the eight input combinations in the order ABC = 000, 001, 010, 011, 100, 101, 110, 111.[2]
(b)The AND gate in this expression is replaced by a single gate whose output is the inverse of AND. Name this gate.[1]
2 marks for all 8 outputs correct; 1 mark for 6 or 7 correct. X is 1 whenever C = 0, and also for A = B = C = 1.
(b) NAND
B1 NAND (NOT AND).
Q2Logic gates & circuits · Core · Paper 1 style · 4 marks
(a)Name the logic gate described by each statement.(i) A two-input gate whose output is 1 only when both inputs are 0.(ii) A two-input gate whose output is 1 only when the inputs are different.(iii) A two-input gate whose output is 0 only when both inputs are 1.(iv) A gate with one input whose output is always the opposite of its input.[4]
Show answer
(a) (i) NOR (ii) XOR (iii) NAND (iv) NOT
1 mark each. Do not accept OR for (iii) — OR gives 0 when both inputs are 0.
Q3Logic gates & circuits · Core · Paper 1 style · 3 marks
(a)Complete the truth table for X = (A XOR B) AND C, for ABC = 000 to 111 in binary order.[2]
(b)State the input combinations that give X = 1.[1]
Q4Logic gates & circuits · Core · Paper 1 style · 4 marks
A warehouse in Karachi has an alarm. Inputs:S = 1 when the alarm system is switched on (armed)D = 1 when a door is openedM = 1 when movement is detectedThe alarm A sounds (A = 1) when the system is armed and either a door is opened or movement is detected.
(a)Write a logic expression for the alarm output A.[2]
(b)Complete the truth table for A, giving A for SDM = 000 to 111 in binary order.[2]
Q5Logic gates & circuits · Core · Paper 1 style · 4 marks
The lift in an office building in Islamabad has a motor controlled by a logic circuit. Inputs:D = 1 when the lift door is closedB = 1 when a floor button has been pressedO = 1 when the lift is overloadedThe motor runs (M = 1) only when the door is closed, a button has been pressed and the lift is not overloaded.
(a)Write a logic expression for M.[2]
(b)Complete the truth table for M for DBO = 000 to 111 in binary order.[2]
Q6Logic gates & circuits · Standard · Paper 1 style · 6 marks
A greenhouse near Murree has an extractor fan controlled by a logic circuit with three inputs:T = 1 when the temperature is too highH = 1 when the humidity is too highW = 1 when the roof window is openThe fan output F = 1 when the window is closed and either the temperature or the humidity is too high.
(a)Write a logic expression for F.[2]
(b)Complete the truth table for F, giving F for THW = 000, 001, 010, 011, 100, 101, 110, 111.[2]
(c)Describe a logic circuit for F that uses exactly three logic gates.[2]
Show answer
(a) F = (T OR H) AND (NOT W)
1 mark for (T OR H); 1 mark for AND NOT W. Accept F = (T AND NOT W) OR (H AND NOT W).
(c) T and H go into an OR gate; W goes into a NOT gate; the outputs of the OR gate and the NOT gate go into an AND gate, whose output is F.
1 mark OR gate with T, H and NOT gate on W; 1 mark both outputs into an AND gate giving F.
Q7Logic gates & circuits · Standard · Paper 1 style · 5 marks
A logic circuit has inputs A, B and C.Gate 1 is a NAND gate with inputs A and B.Gate 2 is a NOR gate with inputs B and C.Gate 3 is an XOR gate whose inputs are the outputs of Gate 1 and Gate 2. Its output is X.
(a)Write the logic expression for X.[2]
(b)Complete the truth table for X for ABC = 000 to 111 in binary order.[3]
Show answer
(a) X = (A NAND B) XOR (B NOR C) [equivalently X = (NOT(A AND B)) XOR (NOT(B OR C))]
1 mark for each bracketed gate correct; XOR must join them.
Working columns: A NAND B = 11111100, B NOR C = 10001000. 3 marks all 8 correct; 2 marks 6–7 correct; 1 mark 4–5 correct.
Q8Logic gates & circuits · Standard · Paper 1 style · 5 marks
A circuit designer in a Lahore electronics firm wants to build every circuit from NAND gates only, because one chip type is cheaper to stock.
(a)Describe how a single NAND gate can be used as a NOT gate.[1]
(b)Describe how A AND B can be produced using only NAND gates. State how many gates are needed.[2]
(c)Describe how A OR B can be produced using only NAND gates.[2]
Show answer
(a) Connect the input to both inputs of the NAND gate (A NAND A = NOT A).
B1 (accept: one input fixed at 1 and the other is the input).
(b) Two NAND gates: A and B go into the first NAND gate; its output goes into both inputs of a second NAND gate (acting as NOT).
1 mark first NAND of A, B; 1 mark second NAND used as NOT, 2 gates.
(c) Three NAND gates: one NAND with both inputs A gives NOT A; one NAND with both inputs B gives NOT B; these two outputs go into a third NAND gate, giving NOT(NOT A AND NOT B) = A OR B.
1 mark inverting A and B separately with NANDs; 1 mark third NAND combining them.
Q9Logic gates & circuits · Standard · Paper 1 style · 4 marks
The doors of a metro train in Lahore close only when at least two of three independent safety sensors A, B and C report that the doorway is clear (sensor output 1 = clear). The output X = 1 closes the doors.Truth table: X = 1 for ABC = 011, 101, 110 and 111; X = 0 for all other combinations.
(a)Write a logic expression for X.[3]
(b)State how many of the eight input combinations give X = 1.[1]
Show answer
(a)X = (A AND B) OR (A AND C) OR (B AND C)(also accepted: X = (NOT A AND B AND C) OR (A AND NOT B AND C) OR (A AND B AND NOT C) OR (A AND B AND C))
3 marks fully correct; 2 marks for three of the four needed terms / two of the three pair terms; 1 mark for one correct term joined correctly with OR.
(b) 4
B1.
Q10Logic gates & circuits · Challenge · Paper 1 style · 6 marks
A circuit uses only two-input NOR gates.Gate 1: inputs A and B, output P.Gate 2: inputs A and P, output Q.Gate 3: inputs B and P, output R.Gate 4: inputs Q and R, output X.
(a)Complete a truth table showing P, Q, R and X for AB = 00, 01, 10, 11.[4]
(b)Name the single two-input gate that would replace the whole circuit.[1]
(c)Explain why a manufacturer might build this function from four NOR gates rather than buying a dedicated gate.[1]
(c) NOR is a universal gate, so a whole circuit can be built from one chip type, reducing cost / stock / board space.
B1 any valid point linked to using a single gate type.
Q11Logic gates & circuits · Challenge · Paper 1 style · 6 marks
(a)Using a truth table with columns A NAND B, A OR B, X1 and A XOR B, show whether X1 = (A NAND B) AND (A OR B) is equivalent to A XOR B.[4]
(b)A student claims that NOT (A AND B) is the same as (NOT A) AND (NOT B). Give one input combination that proves the claim wrong, stating both outputs.[2]
Show answer
(a)A B | A NAND B | A OR B | X1 | A XOR B0 0 | 1 | 0 | 0 | 00 1 | 1 | 1 | 1 | 11 0 | 1 | 1 | 1 | 11 1 | 0 | 1 | 0 | 0X1 and A XOR B are identical in every row, so they are equivalent.
1 mark NAND column; 1 mark OR column; 1 mark X1 column; 1 mark conclusion referring to all rows matching.
(b) For example A = 0, B = 1: NOT(A AND B) = 1 but (NOT A) AND (NOT B) = 0. (A = 1, B = 0 also works.)
1 mark a valid combination (01 or 10); 1 mark both outputs stated correctly.
Q12Logic gates & circuits · Challenge · Paper 1 style · 7 marks
A solar-powered irrigation pump on a farm in Tharparkar is controlled by a logic circuit with four inputs:S = 1 when the soil is dryT = 1 when the storage tank has waterR = 1 when rain is detectedM = 1 when the farmer presses the manual overrideThe pump runs (P = 1) when the tank has water and either the soil is dry and it is not raining, or the manual override is pressed.
(a)Write a logic expression for P.[3]
(b)A truth table for P has 16 rows. State how many rows give P = 1.[2]
(c)The expression can be rewritten with T appearing only once. Write this version and state one advantage of it.[2]
Show answer
(a) P = (S AND T AND NOT R) OR (M AND T)
1 mark S AND T AND NOT R; 1 mark M AND T; 1 mark joined with OR.
(b) 5
M1 counting rows: T must be 1 (8 rows); of these, P = 1 when M = 1 (4 rows) or when M = 0, S = 1, R = 0 (1 row). A1 5.
(c) P = T AND ((S AND NOT R) OR M). It needs fewer gates (one fewer AND gate), so the circuit is cheaper / smaller.
1 mark correct factorised expression; 1 mark advantage.
Q13Input/output devices & sensors · Core · Paper 1 style · 7 marks
A print shop in Rawalpindi uses a laser printer to produce revision booklets for students.
(a)Describe how a laser printer prints a page.[5]
(b)The printer has a buffer. Explain why.[2]
Show answer
(a)Mark points (1 mark each, max 5):• the drum is given an electrostatic charge (by a charge roller / corona wire)• a laser beam scans across the rotating drum• it changes the charge on parts of the drum, forming an electrostatic image of the page• charged toner is attracted to the parts of the drum that form the image• the paper is given a charge so the toner is transferred from the drum to the paper• the fuser unit heats and presses the paper so the toner melts and sticks permanently• the paper/drum is discharged (and the drum cleaned) ready for the next page
Points must be in a sensible order. No mark for 'ink' instead of toner.
(b) The buffer temporarily stores the data waiting to be printed; the computer sends data much faster than the printer can print, so the computer can transfer the whole job to the buffer and continue with other tasks.
1 mark temporary store of print data; 1 mark speed difference / CPU freed.
Q14Input/output devices & sensors · Core · Paper 1 style · 5 marks
An aviation academy in Karachi uses virtual reality (VR) headsets to train pilots.
(a)Describe how a virtual reality headset gives the trainee pilot the feeling of being inside the cockpit.[4]
(b)Give one advantage of training pilots with VR rather than in a real aircraft.[1]
Show answer
(a)1 mark each, max 4:• a screen (or two screens) displays a separate image to each eye• the two images are slightly different, giving a stereoscopic 3D effect• lenses focus/enlarge the images so they fill the field of view• sensors (gyroscope, accelerometer, magnetometer) track head movement• the image is updated to match where the pilot is looking• headphones give sound that matches the scene
(b) e.g. safe to practise emergencies / no fuel cost / repeatable scenarios.
B1.
Q15Input/output devices & sensors · Core · Paper 1 style · 6 marks
(a)Identify the most suitable sensor for each use.(i) Street lights in Faisalabad that switch on automatically at dusk.(ii) A kitchen alarm that warns of a leak from a gas cylinder.(iii) A system that warns when the water depth behind a barrage rises above a safe level.(iv) A shop door that opens when a customer approaches.[4]
(b)State whether the street-light system in (a)(i) is a monitoring system or a control system. Justify your answer.[2]
Show answer
(a) (i) light sensor (ii) gas sensor (iii) pressure sensor (or water level sensor) (iv) infrared / proximity / motion sensor
1 mark each.
(b) Control system: it uses an actuator (switches the lights on/off) to change the output based on sensor input.
1 mark control; 1 mark justification.
Q16Input/output devices & sensors · Standard · Paper 1 style · 5 marks
A dental clinic in Dubai scans patients' teeth and uses a 3D printer to make plastic models for fitting braces.
(a)Describe how a 3D printer produces the model.[4]
(b)Give one benefit to the clinic of printing models rather than ordering them from a laboratory.[1]
Show answer
(a)1 mark each, max 4:• the model is designed with CAD software / scanned to produce a digital design• software slices the design into thin horizontal layers• material (e.g. plastic filament) is heated and melted / liquid resin is used• the print head (nozzle) moves to deposit the material in the pattern of one layer (or a UV laser hardens resin in that pattern)• each layer hardens / cools before the next is added• the object is built up layer by layer from the bottom
Accept other additive methods described accurately.
(b) e.g. models are ready faster / made to the exact scan of each patient / cheaper per model / can be reprinted easily.
B1 any valid benefit.
Q17Input/output devices & sensors · Standard · Paper 1 style · 6 marks
An Urdu-learning app runs on a tablet. Students record themselves reading words using the tablet's microphone and listen to model pronunciation through its speaker.
(a)Describe how the microphone captures a student's speech.[3]
(b)Describe how the speaker plays the recorded model pronunciation.[3]
Show answer
(a)1 mark each, max 3:• sound waves make the diaphragm vibrate• a coil attached to the diaphragm moves within the field of a permanent magnet• this induces a varying electric current / voltage (an analogue signal)• an ADC converts the analogue signal into digital data
(b)1 mark each, max 3:• a DAC converts the digital data to an analogue signal, which is amplified• the varying current flows through a coil, creating a varying magnetic field• this interacts with a permanent magnet, so the coil moves back and forth• the coil moves the cone, which vibrates the air, producing sound waves
Q18Input/output devices & sensors · Standard · Paper 1 style · 6 marks
A hospital in Peshawar uses a computer system in its intensive care unit. It measures patients' vital signs and sounds an alarm at the nurses' station if a reading is outside a safe range.
(a)Explain the difference between a monitoring system and a control system.[2]
(b)Identify two sensors suitable for the intensive care unit system and state what each measures.[2]
(c)Explain why the system needs an analogue-to-digital converter (ADC).[2]
Show answer
(a) A monitoring system reads sensor data and reports it / gives warnings but does not change the conditions; a control system also uses actuators to change the conditions, using feedback from sensors.
1 mark each correct description.
(b) e.g. temperature sensor – patient's body temperature; pressure sensor – blood pressure; (infrared) light sensor – pulse rate / blood oxygen.
1 mark each sensor with matching use.
(c) Sensors produce analogue signals; the computer/microprocessor can only process digital data, so the ADC converts the readings.
1 mark sensor data analogue; 1 mark computer needs digital.
Q19Input/output devices & sensors · Challenge · Paper 1 style · 6 marks
A power company in Gilgit gives its field workers handheld devices for recording meter readings outdoors in winter.
(a)Explain how a capacitive touchscreen detects the position of a touch.[3]
(b)The workers wear thick gloves. Recommend which type of touchscreen should be used and justify your choice.[2]
(c)State one drawback of the type of screen you recommended in (b).[1]
Show answer
(a)1 mark each, max 3:• the screen has a layer of conductive material carrying an electrostatic field / charge• a finger (a conductor) touching the screen changes the capacitance at that point• sensors / circuits around the screen measure the change• a microprocessor calculates the coordinates of the touch from these measurements
(b) Resistive: it detects pressure (two conductive layers pressed together to complete a circuit), so it works with gloved fingers, whereas a capacitive screen needs a conductive touch.
1 mark resistive; 1 mark justification referring to gloves/pressure.
(c) e.g. less sharp/clear image / less responsive / usually single-touch only (no multi-touch gestures) / outer layer more easily scratched.
B1.
Q20Input/output devices & sensors · Challenge · Paper 1 style · 6 marks
A flower grower in Swat uses an automatic computer control system in a greenhouse. It has a temperature sensor, a heater and motor-driven roof vents.
(a)Describe how the system keeps the greenhouse temperature between 22 °C and 26 °C.[6]
Show answer
(a)1 mark each, max 6:• a temperature sensor measures the temperature continuously / at regular intervals• the analogue reading is converted by an ADC• the microprocessor compares the reading with the stored values 22 and 26• if the reading is below 22 °C, it sends a signal to switch on the heater (actuator)• if it is above 26 °C, it sends a signal to an actuator to open the vents / switch on the fan (and switch the heater off)• a DAC may be needed to drive the actuators• feedback: the changed temperature is read again by the sensor, which affects the next output• the process repeats continuously (loop)
Do not award marks for 'the sensor controls the heater' — the microprocessor makes the decision.
Q21Memory & storage · Core · Paper 1 style · 4 marks
(a)Give three differences between RAM and ROM.[3]
(b)State what the ROM in a washing machine is used to store.[1]
Show answer
(a)1 mark each, max 3:• RAM is volatile (contents lost when power off); ROM is non-volatile• RAM can be read and written; ROM is (normally) read only• RAM holds the programs/data currently in use; ROM holds fixed start-up instructions / firmware• RAM is usually much larger in capacity than ROM in the same device
Each difference must state both sides or be clearly comparative.
(b) The firmware / control program (e.g. the wash programs) that runs when the machine is switched on.
B1.
Q22Memory & storage · Core · Paper 1 style · 5 marks
(a)Describe how data is written to and read from a magnetic hard disk.[4]
(b)Give one reason why a solid-state drive (SSD) may be chosen instead of a hard disk for a laptop that is carried every day.[1]
Show answer
(a)1 mark each, max 4:• the disk has platters coated with magnetic material that spin at high speed• a read/write head on an actuator arm moves across the platter to the correct track/sector• to write, the head magnetises tiny areas in one of two directions, representing 1 and 0• to read, the head detects the direction of magnetisation of each area• data is stored in concentric tracks divided into sectors
(b) No moving parts, so it is more robust if dropped / lighter / uses less power / faster access.
B1.
Q23Memory & storage · Standard · Paper 1 style · 4 marks
A laptop sold in Islamabad has 16 GiB of DRAM main memory and 12 MiB of SRAM cache.
(a)Explain why SRAM is used for cache memory and DRAM is used for main memory in this laptop.[4]
Show answer
(a)1 mark each, max 4:• SRAM uses flip-flops/latches and does not need refreshing, so it has faster access times — cache must be fast• SRAM is more expensive per bit / has lower density, so it is only used in small amounts• DRAM stores bits as charge on capacitors, which must be refreshed regularly• DRAM is cheaper per bit and has higher density, so large main memory (e.g. 16 GiB) is affordable
Must link features to the use for full marks.
Q24Memory & storage · Standard · Paper 1 style · 5 marks
A car manufacturer in Karachi fits microcontrollers with programmable ROM into its vehicles.
(a)The engine control unit (ECU) firmware must be updated at the service centre without removing the chip. Identify the most suitable type of ROM and justify your choice.[2]
(b)Describe how an EPROM chip is erased and reprogrammed.[2]
(c)State one limitation of PROM compared with EPROM.[1]
Show answer
(a) EEPROM — it can be erased and reprogrammed electrically while still in the circuit.
1 mark EEPROM; 1 mark in-circuit electrical erase/reprogram.
(b) The chip is removed and exposed to ultraviolet light (through its quartz window), which erases the whole chip; it is then reprogrammed with a special programmer device.
1 mark UV light erases whole chip; 1 mark rewritten using programmer / must be removed.
(c) PROM can only be programmed once; it cannot be erased or reused.
B1.
Q25Memory & storage · Standard · Paper 1 style · 5 marks
A museum in Lahore distributes copies of an archive documentary to schools on Blu-ray discs.
(a)Describe how data is read from an optical disc.[3]
(b)Give two reasons why optical discs are suitable for distributing a museum's archive film to schools by post.[2]
Show answer
(a)1 mark each, max 3:• the disc spins and a laser beam is shone onto the spiral track• the surface has pits and lands• light reflects differently from pits and lands / at transitions between them• a photodetector (light sensor) detects the reflected light and converts it to binary 1s and 0s
(b) e.g. cheap to produce in large quantities; light and robust to post; can be write-once so content cannot be altered/infected; readable in common players.
1 mark each, max 2.
Q26Memory & storage · Challenge · Paper 1 style · 7 marks
A taxi company in Lahore fits dashcams that record video at 8 Mbit/s (1 Mbit = 1 000 000 bits) onto a 64 GiB flash memory card (1 GiB = 2³⁰ bytes).
(a)Calculate the maximum number of whole minutes of video that can be stored on the card. Show your working.[3]
(b)Explain why flash memory is a better choice than a magnetic hard disk for the dashcam.[2]
(c)Describe how a bit is stored in flash memory.[2]
Show answer
(a) 1145 minutes
M1 card size in bits: 64 × 2³⁰ × 8 = 549,755,813,888 bitsM1 divide by 8 000 000 bits per second = 68719.5 sA1 ÷ 60 = 1145.32 → 1145 whole minutes
(b) Flash memory has no moving parts, so it is not damaged by the vibration/bumps of the car; it is also small, light and uses little power.
1 mark no moving parts; 1 mark linked to vibration/size/power in a car.
(c) Each bit is stored by a transistor (floating-gate/charge-trap cell); electrons are trapped in the floating gate (or not), and the presence or absence of trapped charge represents 0 or 1; the charge stays without power.
1 mark charge trapped in floating gate of transistor; 1 mark represents 0/1 and is non-volatile.
Q27Computers & embedded systems · Core · Paper 1 style · 4 marks
(a)Explain what is meant by an embedded system.[2]
(b)Give two examples of devices in a home that contain an embedded system.[2]
Show answer
(a) A computer system (microprocessor/microcontroller with memory) built into a larger device, which performs one dedicated function / a limited set of tasks.
1 mark computer inside a larger device; 1 mark dedicated/specific function.
(b) Any two: washing machine, microwave oven, air conditioner, smart TV remote, digital thermostat, security alarm, refrigerator with controls.
1 mark each.
Q28Computers & embedded systems · Standard · Paper 1 style · 6 marks
An electricity company in Lahore is installing smart meters in homes. Each meter measures energy use every 30 minutes and sends the reading to the company over the mobile network.
(a)Explain why the smart meter is an example of an embedded system. Refer to the scenario.[2]
(b)Give two benefits of using an embedded system in the meter.[2]
(c)Give two drawbacks of using an embedded system in the meter.[2]
Show answer
(a) It contains a microcontroller built into the meter whose only task is to measure the household's electricity use and send the readings to the company — it cannot run general programs.
1 mark built into the meter; 1 mark dedicated function described for this meter. Generic answers ('it is inside') score 0.
(b) e.g. small enough to fit inside the meter; low power consumption; cheap to mass-produce; reliable / runs continuously without user input; readings sent automatically, so no meter reader visits.
1 mark each.
(c) e.g. difficult to upgrade (firmware); connected meter may be hacked; whole unit may need replacing if it fails; limited processing / storage.
1 mark each.
Q29Computers & embedded systems · Standard · Paper 1 style · 4 marks
A supermarket in Hyderabad uses computerised checkouts.
(a)Explain why the checkout computer needs each of the following: input devices, output devices, primary memory and secondary storage. Refer to the supermarket.[4]
Show answer
(a)1 mark each:• input – e.g. barcode scanner to read product codes / card reader for payment• output – e.g. screen showing prices to the cashier/customer, printer for receipts• primary memory – RAM holds the checkout program and the current customer's item list being processed by the CPU• secondary storage – non-volatile storage keeps the software / price file / sales records when power is off
Each point must be linked to the checkout.
Q30Computers & embedded systems · Challenge · Paper 1 style · 6 marks
A car's anti-lock braking system uses a microcontroller connected to sensors on each wheel. If a wheel starts to lock during hard braking, the microcontroller releases and reapplies that wheel's brake many times a second.
(a)Explain why the anti-lock braking system (ABS) is an embedded system.[2]
(b)Explain why the ABS must respond in real time.[2]
(c)The ABS program is stored in non-volatile memory. Explain why, and state one difficulty this causes when the manufacturer finds a bug.[2]
Show answer
(a) The microcontroller is built into the car's braking system and has the single task of monitoring wheel-speed sensors and pulsing the brakes to stop the wheels locking.
1 mark built into braking system/car; 1 mark dedicated function described.
(b) Wheel lock happens in a fraction of a second; if the response is delayed, the wheels lock, the driver loses steering control and the car may crash.
1 mark immediate response needed; 1 mark consequence of delay.
(c) The program must be available immediately every time the car starts without loading it from elsewhere (and must not be lost when power is off); updating it needs special equipment / a visit to a service centre, so many cars may run the faulty version.
1 mark reason for non-volatile; 1 mark difficulty of updating.
Similar questions
Questions that test the same subtopic in different years, grouped so you can work on one skill at a time.
References only: find each question in its paper (official link where available, otherwise through your school).
