G3 Physics and O-Level D.C. Circuits Hub
G3 Physics and O-Level D.C. Circuits hub: circuit symbols, series and parallel rules, whole-circuit calculations, potentiometers, LDRs and NTC thermistors.
Learning goals
- Recognise and interpret circuit symbols for cells, batteries, switches, lamps, LEDs, resistors, fuses, ammeters and voltmeters
- Draw circuit diagrams with cells, batteries, switches, lamps, LEDs, fixed and variable resistors, fuses, ammeters and voltmeters
- Recognise and interpret circuit symbols for d.c. and a.c. supplies, potentiometers, bells, light-dependent resistors and thermistors
- Draw circuit diagrams with d.c. and a.c. supplies, potentiometers, bells, light-dependent resistors and thermistors
- Apply the same-current rule in series circuits
- Apply the potential-difference sum in series circuits
- Apply current conservation at parallel junctions
- Apply equal potential difference across parallel branches
- Calculate effective resistance in series
- Calculate effective resistance in parallel
- Solve whole-circuit problems using consistent quantities
- Describe variable-potential-divider action
- Describe NTC thermistor action as an input transducer
- Describe light-dependent resistor (LDR) action as an input transducer
- Solve simple NTC and LDR potential-divider problems
D.C. Circuits builds from current, potential difference and resistance into complete networks, control circuits and sensor inputs.
Start here
First review Current Electricity. Then study circuit diagrams, series and parallel rules, resistance calculations, the variable potential divider, and sensor dividers in the order below.
The Direct Current & Alternating Current lesson is supporting knowledge. You need the d.c. and a.c. supply symbols here; waveform period and frequency belong to other parts of the course.
What this topic covers
| You need to be able to… | Primary lesson |
|---|---|
| draw circuits using the required sources, controls, meters, resistors, sensors and output components | Electric Circuits & Symbols |
| apply current and potential-difference rules in series and parallel circuits | Series & Parallel Circuits |
| calculate effective resistance and solve a complete circuit | Effective Resistance |
| explain and calculate the action of a variable potential divider | Potential Divider |
| predict how an NTC thermistor or LDR changes a sensor divider’s output | Sensor Potential Dividers |
Lessons
Circuit diagrams
Circuit Symbols
Draw every power-source, control, meter, resistor, sensor and output symbol required by Topic 15.
Series and parallel rules
Series & Parallel Circuits
Apply current and potential-difference rules in both circuit arrangements.
Resistance and whole-circuit calculations
Effective Resistance & Whole Circuits
Reduce resistor networks, apply R = V/I to matching quantities and check the result.
Potential dividers and sensors
Variable Potential Divider
Describe how a potentiometer slider changes the output potential difference.
LDR & NTC Thermistor Dividers
Explain input-transducer action and solve simple sensor-divider problems.
Revision
Use these checks before accepting an answer:
- An ammeter is in series; a voltmeter is across the two points being compared.
- Series: current is the same, p.d.s add and resistances add.
- Parallel: branch p.d.s are equal, branch currents add and effective resistance is below the smallest branch resistance.
- In R = V/I, the R, V and I must describe the same component, branch or whole circuit.
- A divider output trend cannot be decided until the sensor position and output measurement points are known.
Practice
G3 Physics / O-Level practice check
The D.C. Circuits check covers symbols and series rules, parallel circuits and resistance, then potential dividers and sensors, and points you to the lesson to revisit first.
- D.C. Circuits Quiz for rapid checks across the whole topic.
- D.C. Circuits Structured Practice for complete working and multi-step networks.
- Potential Divider Lab for potentiometer, LDR and NTC thermistor output predictions.
Continue learning
Continue to the Practical Electricity Hub to apply circuit reasoning to power, energy, household wiring and electrical safety.
Course and syllabus information
- Course
- SEC G3 Physics
- Edition
- SEC G3 Physics 2027