WJEC A Level Electronics ET4 — Unit Papers & Mark Schemes

Op-amp filter questions require understanding of frequency response. Know the formulae for cut-off frequency (fc = 1/(2πRC)) for first-order active filters, and be able to sketch Bode plots showing gain roll-off at 20 dB per decade. Distinguish between low-pass, high-pass, and band-pass configurations, and explain how the order of the filter affects the steepness of the roll-off. Transistor amplifier questions test biasing calculations. For a common-emitter amplifier, be able to calculate quiescent operating point, voltage gain, input impedance, and output impedance. Understand the role of the bypass capacitor across the emitter resistor (it increases AC gain while maintaining DC stability) and how coupling capacitors block DC between stages. Power electronics questions may present motor control or heating applications. Know the operating principles of thyristors (gate-triggered latching) and triacs (bidirectional switching), and explain how phase-angle control varies the average power delivered to a load.