Generating Electricity
Power Stations
Most UK electricity is generated in power stations using the following sequence: fuel → heat → steam → turbine → generator → electricity.
Thermal power stations (coal, gas, oil, nuclear): burn fuel to heat water, producing steam that spins a turbine connected to a generator. The rotating coil in the generator cuts through a magnetic field, inducing an EMF by electromagnetic induction.
Nuclear power stations: use controlled nuclear fission (usually uranium-235) to generate heat. No CO₂ emissions during operation, but nuclear waste is highly radioactive and long-lived.
Renewable sources (no fuel burnt):
- Wind turbines: wind rotates blades → gearbox → generator. Output fluctuates; needs back-up.
- Solar (photovoltaic): sunlight directly produces electricity in PV cells (no turbine). Produces DC; inverter converts to AC for the Grid.
- Hydroelectric: water falls through a turbine. Very reliable; controllable output; requires suitable geography.
- Tidal / wave: kinetic energy of water; tidal is predictable; wave is less so.
The National Grid
The National Grid transmits electricity from power stations to homes and industry at high voltage using overhead and underground cables. High voltage is used to reduce energy losses.
Power loss in cables: P_loss = I²R. If current I is reduced by a factor of 10, power loss drops by 100. Step-up transformers at the power station increase the voltage (reducing current); step-down transformers near homes reduce the voltage to safe levels (230 V).
Transformers
A transformer changes AC voltage using two coils (primary and secondary) wound on a soft iron core. The changing magnetic flux in the core induces an EMF in the secondary coil (mutual induction). Transformers only work with AC.
Transformer equation: V_s/V_p = N_s/N_p
Where V_p = primary voltage, V_s = secondary voltage, N_p = primary turns, N_s = secondary turns.
Ideal transformer power equation (assuming 100% efficiency): V_p × I_p = V_s × I_s
- Step-up transformer: N_s > N_p → voltage increases, current decreases.
- Step-down transformer: N_s < N_p → voltage decreases, current increases.
Efficiency and Energy Losses
Efficiency = (useful energy output / total energy input) × 100%
Real transformers lose energy through: heat in resistance of windings; eddy currents in the iron core (minimised by laminating the core); magnetisation/demagnetisation cycling in the core.
Environmental Considerations
| Source | Advantages | Disadvantages |
|---|---|---|
| Coal | Reliable, cheap fuel | High CO₂, SO₂; finite |
| Nuclear | No CO₂; high energy density | Radioactive waste; risk of accidents |
| Wind | Renewable, no fuel cost | Unreliable; visual impact; noise |
| Solar | Renewable, silent | Unreliable (night, clouds); land use |
| Hydro | Reliable, controllable | Disrupts ecosystems; limited sites |
⚠Common mistakes
- Transformers work on AC only: a DC supply produces no changing flux, so no EMF is induced in the secondary.
- Forgetting power loss is I²R not IV: it is the current squared that matters, which is why high-voltage (low-current) transmission is so much more efficient.
- Step-up = more current: wrong — step-up increases voltage and decreases current (conservation of power).
- Confusing N_p/N_s ratio: if N_s/N_p = V_s/V_p, then a step-up (V_s > V_p) needs N_s > N_p.
AI-generated · claude-opus-4-7 · v3-wjec-physics