S3 Physics – Electricity 2 (Electronics & Control)

Overview

In Electricity 2 we move from “just circuits” to electronics and control. You’ll learn how a potential divider can turn changes in light or temperature into a useful output, how to power an LED safely, and how a circuit can switch at the right moment.

The same ideas keep coming back: resistance changes → voltages change → output changes. By the end of this unit, you’ll be reading the hidden language of control circuits — using diagrams, measurements, and real builds you can test.

🔗 Key links

Start with the Knowledge Organiser (symbols + rules), then use your booklet.

🧠 Knowledge Organiser (B2) MAIN

Symbols, divider rules, tools/testing box — start here.

📘 Electricity 2 Booklet (B2) practice

Do sections, get checked, then move on.

⚡ Physics Past Paper Finder mixed Qs

Use after KO + methods (not just calculations).

💡 Electronics PPQ Section C

Great for symbols, switching, simulation, safety & tools.

✅ What to attempt (tap to open)tap to open

Physics: focus on Voltage, Ohm’s Law, Circuit rules.
Electronics: symbols & functions, resistor values, series/parallel, switching circuits, voltage dividers, simulation/testing, safety, errors, layout/diagrams.
Note: you may see a few unfamiliar symbols (mix of S3 + N5 Electronics).

▶ Video revision (watch only what you need)

Open a video to load it. Watch → then go straight to booklet questions.

Voltage Divider Theorytap to load

Voltage Divider Theory

How changing resistor values changes the output voltage.

LEDs – Basictap to load

LEDs – Basic

Why LEDs need a protective resistor.

Thermistors and LDRstap to load

Thermistors and LDRs

How sensors change resistance.

Transistor Switching Circuitstap to load

Transistor Switching Circuits

Using a transistor as a switch.

Stripboard Schematicstap to load

Stripboard Schematics

Plan track cuts and links before soldering.

🧾 Test details (no spoilers)

What to expect

3 sections in total.
Section 1: 5 multiple choice questions.
Section 2: Physics written questions — 15 marks.
Section 3: Electronics written questions — 10 marks.
Total time: 45 minutes.

Time strategy

Do the easy marks first (build confidence).
If stuck: write what you do know (often earns marks).
Leave ~5 minutes at the end to check units, polarity and sensible answers.

General advice: Use the KO for symbols and rules, and practise explaining control/switching in full sentences.

🎯 Success criteria (G / A / R) — saved on this device

Tap each statement and choose G, A or R. Use the summary to decide what to do next.

Tip: If you mark something Red, pick one action: KO → worked example → practise → ask for help.

💡 LED tool (protective resistor ↔ current)

Use this to either: (1) calculate the protective resistor for an LED, or (2) calculate the current if you already know the resistor.

Mode

Supply voltage, V_s (V)

LED forward voltage, V_LED (V)

LED current, I (mA)

Resistor series (suggestion)

Step 1: V_R = V_s − V_LED = —

Step 2: I (A) = I (mA) ÷ 1000 = —

Step 3: R = V_R ÷ I = —

Suggested resistor: next highest available → —

If V_s ≤ V_LED, the LED won’t run properly from that supply.

🎯 LED practice (random + check your answer)tap to open

Try working it out yourself first, then check. (We accept ±5%.)

Practice V_s (V)

Practice V_LED (V)

Practice I (mA)

My resistor answer (Ω)

Series for suggestion

🎛️ Interactive switching circuits (4 types)

Build a perfect cause → effect explanation. Choose a circuit type, then press Check.

✅ Switching sentence buildertap to open

Circuit type

When the temperature , the resistance of the thermistor .

The voltage across the thermistor , and the voltage across the variable resistor .

When this reaches the , the transistor and LED .

⭐ Quick science remindertap to open

LDR: more light → lower resistance.
NTC thermistor: higher temperature → lower resistance.
In a divider: if a component’s resistance decreases, the voltage across it decreases too (and the other part increases).

🧰 Electronics skills & testing (must-know)

These are common written questions (short bullet points = full marks).

🧪 Testing, meters, safety, toolstap to open

Pre-power checks (examples)

Correct component values (especially resistors).
Correct polarity (LED/diode/capacitor/transistor/MOSFET).
No short circuits / no solder bridges.
Rails correct (V+ and 0V continuous).

Functionality tests (examples)

Supply voltage correct at rails.
Vout changes as expected with light/temp.
Output switches at the intended point.
Nothing heats unexpectedly; current not excessive.

Meter rules

Voltmeter: in parallel (measures V across a component).
Ammeter: in series (measures current through a circuit).
Resistance: power OFF to measure.

Tool functions

Track cutter: breaks copper track on stripboard.
Heat sink: protects heat-sensitive parts while soldering.
Solder sucker: removes molten solder to fix mistakes/clear holes.

Mark-friendly writing: answer practical questions in short bullet points (2 clear points = full marks).

⚡ S3 Physics – Electricity 2: Electronics & Control

Overview

🔗 Key links