Electricity
Current, potential difference and resistance, series and parallel circuits, mains electricity and electrical power.
Learn
Electricity, explained point by point
Everything the GCSE specification expects you to be able to do, and how to actually do it - the same lesson a signed-in student studies from.
Describe charge and current
Electric current is the flow of charge round a circuit, measured in amps. Charge, current and time are linked by Q = It, so a current of 2 A for 30 seconds moves 60 coulombs of charge. Current is the same everywhere in a single loop because charge is not used up on the way round.
Use potential difference and resistance (V = IR)
Potential difference (voltage) is the energy given to the charge, measured in volts, and resistance opposes the current, measured in ohms. They connect through V = IR. So 6 V across a 3 Ω resistor drives a current of 6 ÷ 3 = 2 A. A higher resistance means a smaller current for the same voltage.
Compare series and parallel circuits
In series, components share one loop: the current is the same all round and the voltages add up to the supply. In parallel, components sit on separate branches: each gets the full supply voltage and the branch currents add up. That is why home lights are wired in parallel - one can switch off without the rest going dark.
Interpret I–V characteristics of components
Plotting current against voltage reveals a component's behaviour. A fixed resistor gives a straight line through the origin - resistance is constant. A filament lamp curves as it heats up and its resistance rises. A diode lets current flow one way only. Recognising each graph is a common exam task.
Calculate electrical power and energy
Electrical power is P = VI, and combining with V = IR also gives P = I²R. A device using 230 V at 2 A has a power of 460 W. Energy transferred is power × time (E = Pt), which is how your electricity bill is worked out - from the power of each appliance and how long it runs.
Describe mains electricity and the National Grid
Mains electricity in the UK is alternating current (a.c.) at 230 V and 50 Hz, unlike the direct current from a battery. The National Grid moves electricity from power stations to homes; transformers step the voltage up to reduce energy wasted over long cables, then step it back down for safe use.
Electricity key terms
The words the specification and the mark schemes use, each defined the way an examiner wants it.
- Electric charge
- The property of matter that electricity is made of, carried by electrons in circuits. Measured in coulombs: charge = current × time (Q = It).
- Electric current
- The rate of flow of electrical charge, measured in amperes. In a single closed loop, the current is the same at every point.
- Potential difference
- The energy transferred per unit of charge passing between two points in a circuit, measured in volts.
- Resistance
- How much a component opposes the flow of current, measured in ohms. Potential difference = current × resistance (V = IR).
- Series circuit
- A circuit with components in a single loop: the same current flows through every component, and the source potential difference is shared between them.
- Parallel circuit
- A circuit with components on separate branches: the potential difference across each branch is the same, and the current splits between them.
- Direct and alternating current
- Direct current (from cells and batteries) flows in one direction. Alternating current (mains electricity, 230 V and 50 Hz in the UK) repeatedly reverses direction.
- The National Grid
- The country-wide system of cables and transformers that carries electricity from power stations to homes and businesses.
Practice
Try a Electricity question
A GCSE-style original question from this topic. Have a go before you open the working - deciding on an answer first is what makes the working stick.
A current of 3 A flows through a 10 Ω resistor. Use P = I² × R to work out the power dissipated, in watts (W).
- 30
- 900
- 90
- 3.3
Show the answer and the working
Answer: 90
Square the current first, then multiply by the resistance: P = 3² × 10 = 9 × 10 = 90 W.
- The power equation using current and resistance is P = I² × R.
- Square the current first: 3² = 9.
- Multiply by the resistance: P = 9 × 10 = 90.
- So the power dissipated is 90 W.