This mini-lesson walks you through the core 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.
Make a guess: what does the bulb take from the charge?
Mission 1What does a bulb take from the charge?
Mission 2How can more resistance mean less?
Mission 3Hairdryer or bulb: which transfers more energy?
Mission 4What saves you from a live kettle?
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.
Q = I × tcharge (C) = current (A) × time (s) ⇄ I = Q ÷ 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.
In a single loop the current is the same at every point: charge is not used up as it flows round.
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
Prescribed Practical P7: place a metal wire in series with an ammeter and a variable resistor, with a voltmeter across it. Use small currents and switch off between readings so the wire stays at a constant temperature. Vary the current, record V and I, then plot V against I — a straight line through the origin (Ohm's law), so R = V ÷ I is constant.
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.
Mission 1 check
What does a bulb take from the charge?
?A car headlamp is lit. An ammeter in the wire going into the lamp reads 4 A. What does an ammeter in the wire coming out read, and what does the lamp take?
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?
Mission 2 of 4
How can more resistance mean less?
Make a guess: how can adding a resistor lower the total resistance?
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?
Mission 2 check
How can more resistance mean less?
?A 12 Ω resistor is connected to a cell. A second 12 Ω resistor is then connected in parallel with it. What happens to the total resistance?
Mission 3 of 4
Hairdryer or bulb: which transfers more energy?
Make a guess: which one transfers more energy each day?
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 = I²RBeyond CCEA — handy when you know the current and resistance but not the voltage, though CCEA only lists P = V × I.
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.
Mission 3 check
Hairdryer or bulb: which transfers more energy?
?A 2400 W kettle is used for 150 s each day. A 6 W Wi-Fi router is on all day, which is 86 400 s. Which transfers more energy each day?
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.
Mission 4 of 4
What saves you from a live kettle?
Make a guess: what saves you when the kettle's metal case becomes live?
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, going through 50 complete cycles every 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.
Mission 4 check
What saves you from a live kettle?
?Inside a metal toaster, the live wire works loose and touches the metal case. The plug is wired correctly with a fuse. What happens next that keeps the user safe?
Recap
The equations to know
Charge: Q = I × t
Ohm's law: V = I × R
Power: P = V × I (P = I²R is not on the CCEA list)
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 the core of CCEA Electricity — symbols, circuits, the I–V characteristics, power & energy and mains safety. Press Finish to see your score.
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Mini-lesson complete!
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You've worked through Electricity for CCEA GCSE Physics. 🎉