Mains power supply systems: the transformer, rectifier, reservoir smoothing and regulation stages, ripple voltage, and series and switch-mode regulators.

Turns ratio (up to 2 marks): for an ideal transformer $\dfrac{N_p}{N_s} = \dfrac{V_p}{V_s} = \dfrac{230}{12} = 19.2$, so about $19:1$.

Peak DC output (up to 2 marks): the reservoir capacitor charges to the peak of the secondary voltage, $V_\text{peak} = V_\text{rms}\sqrt{2} = 12 \times \sqrt 2 = 17\ \text{V}$ (a little less once diode drops are included).

Effect of load (up to 2 marks): a larger load current discharges the reservoir capacitor faster between peaks, so the ripple voltage increases (the output sags more before the next charging pulse).

Markers reward the turns ratio $19:1$, the peak output $17\ \text{V}$ from $V_\text{rms}\sqrt 2$, and the statement that more load current means larger ripple.

Linear (series) regulator (up to 2 marks): it drops the excess voltage across a series transistor controlled by feedback, holding the output constant. Advantage: it is simple and produces a very clean, low-noise output with little electrical interference.

Switch-mode regulator (up to 2 marks): it rapidly switches the input on and off and uses an inductor and capacitor to store and average the energy, controlling the output by the switching duty cycle. Advantage: it is far more efficient (typically 85 to 95 per cent) because the switching transistor dissipates little, so it runs cool and suits high-power or battery use.

Conclusion (up to 1 mark): linear regulators are chosen for low noise and simplicity at low power; switch-mode regulators are chosen for efficiency at higher power.

Markers reward the series-pass versus switching mechanism, low noise as the linear advantage, and high efficiency as the switch-mode advantage.