GCSE Electricity Revision ⚡

⚡ Current, Charge & Voltage

Everything you need to understand what electricity actually IS.

💬 "Voltage is the pressure, current is the flow, resistance is your annoying older sibling blocking the way."

Current (I) — the flow of electric charge. Measured in Amperes (A). Think of water flowing through a pipe.

Voltage (V) — the "push" that drives the current. Measured in Volts (V). Think of water pressure.

Resistance (R) — opposition to current flow. Measured in Ohms (Ω). Think of a narrow pipe slowing the water.

Q = I × t

Charge (C) = Current (A) × time (s)

Live charge calculator: adjust current and time

Current I: 2.0 A

Time t: 5 s

Charge Q =

10 C

Charge counter: 0 C of charge has flowed

🔁 Ohm's Law — V = IR

The most important equation in electricity. Lock any one, the others calculate. Pure magic.

💬 "V=IR is the V.I.R.tually perfect equation. Sorry."

Cover what you want to find

V = I × R | I = V / R | R = V / I

🔒 Lock one value — the other two will calculate

Voltage (V)

12.0

Current (A)

2.4

Resistance (Ω)

5.0

Voltage V: 12.0 V

Current I: 2.4 A

Resistance R: 5.0 Ω

➡️ Series Circuits

One path for the current. No choices, no branches — like a one-way street.

Current same everywhere: I_total = I₁ = I₂

Voltages add up: V_supply = V₁ + V₂

Resistances add up: R_total = R₁ + R₂

Supply voltage: 12 V

R1: 4 Ω

R2: 8 Ω

⑂ Parallel Circuits

Multiple paths for the current. More routes = more current can flow.

Voltage same across each branch: V₁ = V₂ = V_supply

Currents add up: I_total = I₁ + I₂

Total resistance less than smallest branch: 1/R_t = 1/R₁ + 1/R₂

Supply voltage: 12 V

R1: 4 Ω

R2: 12 Ω

💡 Power — P = IV

How fast a component converts electrical energy. The higher the power, the more energy per second.

P = IV

Power (W) = Current (A) × Voltage (V)

P = I²R

Power = Current² × Resistance

P = V²/R

Power = Voltage² ÷ Resistance

💬 "Why does a thin wire get hotter? P = I²R — thin wire = high R = lots of power wasted as heat. That's the fuse working as intended."

Current I: 3.0 A

Voltage V: 230 V

Resistance R: 25 Ω

P = IV

690 W

P = I²R

225 W

Note: I²R ≠ IV when R isn't the only resistance in the circuit

📈 I-V Characteristics

Plot current against voltage — the graph shape tells you EVERYTHING about a component.

🌡️ Resistance & Special Components

LDRs and thermistors change their resistance depending on the environment. Brilliant for sensors.

💡 LDR — Light Dependent Resistor

Light level: 50%

Use: Burglar alarms (bright light = low R = current flows = alarm triggers). Street lights (dark = high R = switch on).

🌡️ Thermistor

Temperature: 20°C

Use: Thermostats (hot = low R = more current = heating turns off). Fire alarms, baby monitors.

🔌 Mains Electricity & Safety

230V AC. Three wires. One fuse. These are the things that keep you alive.

💬 "The earth wire is the one that saves your life. Brown bites, blue neutral, green-and-yellow is your guardian angel."

AC vs DC

UK Plug Wiring

🔴 Live (Brown) — carries the 230V. Don't touch.

🔵 Neutral (Blue) — completes the circuit. Return path.

🟢 Earth (Green/Yellow) — safety. Diverts fault current to ground.

🔥 Fuse Animation

Current through fuse: 3 A

⚡ Static Electricity

Charge buildup on insulators — responsible for lightning, photocopiers, and that awkward moment with a doorknob.

Same charges repel. Opposite charges attract.

Uses: Inkjet printers, electrostatic paint sprayers, defibrillators, photocopiers

Dangers: Fuel tankers (earthing strap needed), lightning strikes

✅ Quiz — Test Yourself

Five questions covering the key topics. No peeking at the equations panel. (Well, maybe just a quick peek.)

1. A circuit has a voltage of 12 V and a resistance of 4 Ω. What is the current?

I = V ÷ R = 12 ÷ 4 = 3 A. Rearrange V = IR → I = V/R.

2. In a series circuit with two resistors, which statement is correct?

In a series circuit, there's only one path. The same current flows through every component. Voltage splits across resistors, but current stays constant.

3. A kettle draws 13 A from a 230 V supply. What is its power?

P = IV = 13 × 230 = 2990 W (about 3 kW — which is typical for a kettle!).

4. Which component has resistance that DECREASES as temperature increases?

A thermistor decreases in resistance as temperature rises — more thermal energy frees more charge carriers. An LDR decreases in resistance as light increases. A filament bulb INCREASES resistance as it heats up.

5. A UK plug has a 13 A fuse but the appliance only needs 5 A. The fuse rating should be…

A fuse should be rated just above normal operating current. For a 5 A appliance, use a 3 A fuse (standard UK ratings are 3 A and 13 A). Too big = won't blow in a fault. Too small = blows in normal use.

Electricity Equations

V = IRVoltage = Current × Resistance

P = IVPower = Current × Voltage

P = I²RPower = Current² × Resistance

P = V²/RPower = Voltage² ÷ Resistance

Q = ItCharge = Current × time

E = QVEnergy = Charge × Voltage

R_series = R₁+R₂Series total resistance

1/R_par = 1/R₁+1/R₂Parallel total resistance

GCSE Electricity ⚡