This mini-lesson walks you through the whole of CCEA Electricity: circuit symbols, charge & current, potential difference and resistance, the I–V characteristics, series vs parallel rules, power & energy, the kilowatt-hour and mains safety.
Electricity is the flow of charge round a circuit. Work through each screen and collect ⭐ stars. Press Start.Circuit symbols
The symbols you must know
A circuit diagram is a "visual shorthand". CCEA expects you to recognise and draw these standard symbols:
A cell's long line is +, short line is −. An ammeter goes in series; a voltmeter in parallel. A diode lets current flow one way only (arrow = flow direction).Quick check
Name that symbol
?Which component is drawn as a triangle pointing at a line, and only lets current flow in one direction?
Charge & current
Current is the flow of charge
An electric current is the rate of flow of charge — in a metal wire, a flow of free electrons. The more charge that passes a point each second, the bigger the current.
I = Q ÷ tcurrent (A) = charge (C) ÷ time (s) ⇄ Q = I × t
Charge Q is measured in coulombs (C), current I in amperes (A), time t in seconds (s). Current is measured with an ammeter in series.
Worked example
A current of 3 A flows for 20 s.
Q = I × t = 3 × 20 = 60 C
Direction:conventional current flows from + to − outside the cell, even though the electrons themselves drift the opposite way.
Calculate
Your turn — charge
1A current of 0.5 A flows through a lamp for 40 s. Calculate the charge that passes through it.
C
Hint: Q = I × t = 0.5 × 40.
Potential difference & resistance
Voltage pushes, resistance opposes
Potential difference (p.d., or voltage) is the energy transferred per unit charge between two points — measured in volts (V) with a voltmeter in parallel. Resistance opposes the current and is measured in ohms (Ω).
V = I × Rpotential difference (V) = current (A) × resistance (Ω) ⇄ R = V ÷ I
Required practical: place a component in series with an ammeter and a variable resistor, with a voltmeter across it. Vary the current, record V and I, then plot V against I or work out R = V ÷ I.
Worked example
A resistor carries 0.4 A when the p.d. across it is 6 V.
R = V ÷ I = 6 ÷ 0.4 = 15 Ω
Calculate
Your turn — resistance
2The p.d. across a resistor is 12 V and the current through it is 0.25 A. Calculate its resistance.
Ω
Hint: R = V ÷ I = 12 ÷ 0.25.
I–V characteristics
How current depends on voltage
Plotting current (I) against potential difference (V) gives a component's I–V characteristic. The shape tells you how its resistance behaves:
Ohmic resistor (at constant temperature): a straight line through the origin — R is constant. Filament lamp: an S-shaped curve — as current rises the filament heats up, so its resistance increases and the line bends over.Diode: almost no current until the forward voltage is reached, then it rises sharply; in reverse it stays near zero (very high resistance).Quick check
Reading the graph
?An I–V graph is a straight line passing through the origin. What does this tell you about the component?
Sensors: LDR & thermistor
Resistance that responds
Two components change their resistance with their surroundings — handy for sensing circuits:
LDR (light-dependent resistor): resistance is high in the dark and falls as it gets brighter — used to switch lights on at dusk.
Thermistor: resistance is high when cold and falls as it gets hotter — used in thermostats and temperature sensors.
For both, more light / heat means less resistance.Quick check
Sensor behaviour
?What happens to the resistance of a thermistor as it gets hotter?
Series vs parallel
Two ways to wire components
How components are connected changes how current and voltage behave. CCEA wants the rules for both:
Left: a series circuit — ammeter in series. Right: a parallel circuit — voltmeter in parallel across a lamp.
Series: current is the same everywhere · p.d.s add up to the supply · total resistance = R₁ + R₂ + …
Parallel: p.d. is the same across each branch · branch currents add up to the total · total resistance is less than the smallest single resistor.
Misconception: in a series circuit the current is not "used up" by the first lamp — it is the same at every point. It is the voltage that splits between the components.
Sort it
Series or parallel rule?
Tap a statement, then tap the circuit type it describes.
🔗 Series
🪢 Parallel
Quick check
Splitting the current
?In a parallel circuit the supply provides 0.9 A. One branch draws 0.6 A. How much flows in the only other branch?
Electrical power
Power in a circuit
Electrical power is the rate at which a component transfers energy:
P = V × Ipower (W) = potential difference (V) × current (A)
Because V = IR, you can also write P = I²RHigher — useful when you know the current and resistance but not the voltage.
Worked example
A heater runs at 230 V drawing 4 A.
P = V × I = 230 × 4 = 920 W
Calculate
Your turn — power
3A lamp operates at 12 V and draws a current of 2 A. Calculate its electrical power.
W
Hint: P = V × I = 12 × 2.
Electrical energy
Energy transferred
The energy a component transfers depends on the power and how long it runs:
E = V × I × t = P × tenergy (J) = power (W) × time (s)
Run a high-power appliance for a long time and it transfers a lot of energy — which is exactly what shows up on the electricity bill.
Worked example
A 2000 W kettle runs for 90 s.
E = P × t = 2000 × 90 = 180 000 J (180 kJ)
Calculate
Your turn — energy
4A 60 W lamp is left on for 300 s. Calculate the energy it transfers.
J
Hint: E = P × t = 60 × 300.
Kilowatt-hour & cost
Paying for electricity
Joules are tiny for household use, so energy companies bill in kilowatt-hours (kWh) — the "units" on your meter. One kilowatt-hour is the energy used by a 1 kW appliance running for 1 hour.
units (kWh) = power (kW) × time (h)cost = units (kWh) × price per unit
Watch the units: power must be in kilowatts (÷ 1000) and time in hours before you multiply.
Worked example
A 2 kW heater runs for 3 h; electricity costs 30p per unit.
5A 1.5 kW iron is used for 2 hours. Electricity costs 24p per unit (kWh). Calculate the total cost in pence.
p
Hint: units = 1.5 × 2 = 3 kWh, then × 24p.
Mains electricity
a.c., d.c. and the three-pin plug
A cell gives direct current (d.c.) — charge flows one way. The UK mains supply is alternating current (a.c.) at about 230 V, reversing direction 50 times a second (50 Hz).
Live = brown (carries the supply, and the fuse sits here). Neutral = blue (completes the circuit). Earth = green/yellow (safety, to the longest top pin).Electrical safety
Fuses, earthing & insulation
Fuse: a thin wire in the live wire that melts if the current gets too high, breaking the circuit and protecting the cable and appliance.
Earthing: a metal case is connected to the earth wire, so a fault sends a large current to earth, blowing the fuse before anyone is shocked.
Circuit breaker: a switch that trips and cuts the current; unlike a fuse it can be reset, and it acts faster.
Double insulation: an appliance with a plastic case and no exposed metal needs no earth wire (marked with the double-square symbol).
Misconception: a fuse does not protect you directly — it protects the cable and appliance by cutting the current. The earth wire + fuse working together keep the user safe from a metal case becoming live.
Match-up
Safety features
Tap a safety feature on the left, then its correct job on the right.
Recap
The equations to know
Charge: Q = I × t
Ohm's law: V = I × R
Power: P = V × I (= I²R, Higher)
Energy: E = V × I × t = P × t
Cost: units (kWh) = power (kW) × time (h); cost = units × price
Series: same I, p.d.s add · Parallel: same p.d., currents add
You've covered CCEA Electricity end to end — symbols, circuits, the I–V characteristics, power & energy and mains safety. Press Finish to see your score.
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