Key Idea: Every electronic product is input → process → output, with a power supply feeding all three and often feedback returning to the process. Find those four on the board and you have analysed it. V = IR and P = VI, rearranged both ways, and mA and kΩ turned into A and Ω before substituting. Series shares one current and splits the voltage; parallel shares one voltage and splits the current. Total resistance in parallel is always smaller than the smallest branch. A flow chart is the program drawn: start/stop, process, decision with labelled branches, and a loop back. A sensor is chosen by what it senses, its range, its resolution and its output — and an output device by what the user must notice.
Paper 1 — multiple choice
- Calculate a current, a voltage or a power
- Find the total resistance of a series or parallel pair
- Read a logic gate or a truth table
- Identify a symbol, a sensor or an output device
Paper 2 — analysing a product
- Name the input, process, output and power stages of a real product
- Choose a sensor for a stated job and justify it
- Construct a flow chart for the product's behaviour
- Explain why the product uses a particular communication protocol
Carried into the design project
- Criterion D — a circuit claim needs a measured reading, not a datasheet
- Photograph your breadboard with the meter in shot
- Record what the product does when the sensor fails
Almost every Paper 2 electronics question is the same question asked about a different product: what senses, what decides, what acts, what powers it, and whether anything checks the result.
| Stage | What to look for | The answer that scores |
|---|---|---|
| Input | Anything that turns a physical quantity into a voltage — a switch, an LDR, a thermistor, a microphone | Name the component AND what it senses, not just 'a sensor' |
| Process | The microcontroller, the logic gate, the op-amp, the comparator | Say what decision it makes and on what basis |
| Output | Motor, LED, buzzer, speaker, heater, display | Say what the user notices, and how the output is driven |
| Power | Battery, mains adaptor, regulator, the wide tracks on the board | Give a voltage — a 3 V coin cell and a 230 V mains product are different designs |
| Feedback | Anything that measures the result and feeds it back | If nothing does, say so — open loop is an answer, not a gap |
Series and parallel side by side, with the shared quantity and the split quantity marked on each.
🔒 Interactive diagram
Explore the labelled diagram, charts and maps for this topic in study mode.
Important: Milliamps and kilohms left in a V = IR calculation. Parallel resistance added like series — it is always smaller than the smallest branch. A decision diamond with unlabelled branches in a flow chart. Every one needs its yes and its no. 'A sensor' as an answer where the question wanted a named sensor, its range and its output.
| Choice | What decides it | The justification that earns the mark |
|---|---|---|
| Sensor | Quantity, range, resolution, output type, cost | 'A thermistor, because it covers 0-100 °C and gives a resistance a microcontroller can read directly' |
| Output device | What the user must notice, and in what conditions | A buzzer works in the dark and across a room; an LED does not, but is silent in a hospital ward |
| Protocol | Distance, data rate, power budget, whether it must reach the internet | Bluetooth Low Energy for a wearable; Wi-Fi only if the product must reach a server itself |
| Logic | How many inputs, and what combination must act | AND for two conditions together, OR for either, NOT to invert a sense |
| Flow chart | The behaviour, drawn | Start, inputs, a decision with LABELLED branches, outputs, and a loop back to the start |
The five flow-chart symbols on one working program, with both branches of every decision labelled.
🔒 Interactive diagram
Explore the labelled diagram, charts and maps for this topic in study mode.
Series shares current; parallel shares voltage. Parallel total < the smallest branch — the fastest check there is. P = VI, so a 12 V 2 A motor takes 24 W and the supply must give it. An LDR falls in light; a thermistor (NTC) falls when warm. A decision diamond has exactly two labelled exits.
A cycle light runs from a 6 V supply. It has three LEDs in parallel, each drawing 20 mA through its own 150 Ω resistor. Apply the circuit equations to find the total current, the total power and the resistor dissipation.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
A greenhouse vent opener must open a vent when the air is above 26 °C AND the soil is not dry. Construct the system and a flow chart for it.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
A wearable heart-rate band uses Bluetooth Low Energy rather than Wi-Fi. Justify that choice.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
What are the four stages to find in any electronic product?
What is shared and what is split in series and parallel?
State the two equations and their units.
What makes a flow chart correct rather than approximate?
How do you justify a sensor choice?
Why is a transistor or relay between a controller and a motor?
Exam tips
- Answer in the order input, process, output, power, feedback — it is the mark scheme's order.
- Convert mA to A and kΩ to Ω before substituting.
- Check any parallel total is smaller than the smallest branch.
- Label both exits of every decision diamond.
- Name the actual component, never 'a sensor' or 'a chip'.
- Give a voltage when you mention the power supply.