How electric charge flows, how circuits work, and the rules that make electrical systems predictable

Electricity is one of the most important topics in GCSE Physics. It explains how current flows, how components behave, and how electrical energy is transferred and controlled.

Once students understand current, voltage, resistance, and circuit behaviour, the rest of physics, from electromagnetism to energy, becomes far more intuitive.

GCSE Exam Essentials

Students must be able to:

• Describe current, potential difference, and resistance
• Use the equation V = IR
• Interpret series and parallel circuits
• Understand charge, energy, and power equations
• Describe the National Grid and mains electricity
• Explain AC vs DC
• Understand fuses, circuit breakers, and safety features
• Interpret circuit diagrams and component characteristics

These appear across AQA, Edexcel, and OCR GCSE Physics specifications.

1. Current, Potential Difference and Resistance

Current (I)

The flow of electric charge. Measured in amperes (A).

Potential Difference (V)

The energy transferred per unit charge. Measured in volts (V).

Resistance (R)

How much a component opposes the current. Measured in ohms (Ω).

“Potential difference pushes charge around; resistance opposes it.”

2. Ohm’s Law

The core equation of GCSE electricity:

• If voltage increases, current increases.
• If resistance increases, current decreases.

This is used in almost every exam question.

3. Series and Parallel Circuits

Series Circuits

• Current is the same everywhere
• Voltage is shared between components
• Adding components increases resistance

If one component breaks → the whole circuit stops.

Parallel Circuits

• Voltage is the same across each branch
• Current splits between branches
• Adding branches reduces total resistance

If one branch breaks → others continue working.

This is why household circuits use parallel wiring.

4. Charge, Energy and Power

Charge

Charge = current × time. Measured in coulombs (C).

Energy Transferred

or

Measured in joules (J).

Power

or

Measured in watts (W).

These equations are essential for appliance and mains electricity questions.

5. Component Characteristics

Students must interpret I–V graphs for:

Resistor

• Straight line
• Obeys Ohm’s law

Filament Lamp

• Curve
• Resistance increases as temperature rises

Diode

• Current flows in one direction only

These graphs appear frequently in exams.

6. Mains Electricity and the National Grid

AC vs DC

• AC (alternating current) mains supply changes direction
• DC (direct current) batteries, one direction only

UK mains supply:

• 230 V
• 50 Hz

National Grid

Transfers electricity from power stations to homes.

Uses:

• Step‑up transformers → increase voltage, reduce current, reduce energy loss
• Step‑down transformers → reduce voltage for safe domestic use

7. Electrical Safety

Three‑pin plug

• Live wire (brown) carries alternating potential
• Neutral wire (blue) completes the circuit
• Earth wire (green/yellow) safety path

Fuses and circuit breakers

Protect against excessive current.

8. Common Misconceptions (GCSE‑specific)

Students often:

• Think current is “used up” (it is the same in series circuits)
• Mix up voltage and current
• Forget that resistance increases in series but decreases in parallel
• Confuse AC and DC
• Think the earth wire normally carries current (it doesn’t)

“Thinking current is used up” “Confusing voltage and current”

9. Quick Check Questions

Use these for active recall:

1. What is the equation linking voltage, current, and resistance?
2. How does current behave in a series circuit?
3. What is the UK mains voltage?
4. Why are step‑up transformers used in the National Grid?
5. What does a diode do?

10. Summary

Electricity explains how charge flows and how circuits behave. Understanding current, voltage, resistance, and circuit design provides the foundation for later topics such as electromagnetism, waves, and energy transfer.