What this topic covers

Alternating currents is topic 21 of the Cambridge 9702 syllabus (2025–2027), covering the characteristics of alternating currents and rectification and smoothing. It is A Level content, examined in Paper 4 (A Level Structured Questions), which carries 38.5% of the A Level. Students most often find it difficult to distinguish peak values from root-mean-square values, to explain why the r.m.s. value is used for power calculations, and to recall that mean power in a resistive load is half the peak power for a sinusoidal supply. Rectification questions require accurate sketches of half-wave and full-wave outputs, including the bridge rectifier, and an understanding of how a smoothing capacitor and the time constant affect ripple. The topic is compact but examined with precision.

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Questions in this topic

• 9702/41/O/N/24 Q6 — Rectification and circuits · 11 marks
• 9702/42/O/N/24 Q8 — Alternating current · 9 marks
• 9702/43/O/N/24 Q6 — Rectification and circuits · 11 marks
• 9702/43/M/J/24 Q7 — AC circuits and power dissipation · 10 marks
• 9702/41/O/N/23 Q7 — power in AC circuits · 8 marks
• 9702/43/O/N/23 Q7 — power in AC circuits · 8 marks
• 9702/41/M/J/23 Q5 — half-wave rectification · 9 marks
• 9702/42/M/J/23 Q7 — Bridge rectifier circuit · 10 marks
• 9702/43/M/J/23 Q5 — half-wave rectification · 9 marks
• 9702/41/O/N/22 Q7 — AC circuits and piezoelectric effect · 10 marks
• 9702/43/O/N/22 Q7 — AC circuits and piezoelectric effect · 10 marks
• 9702/41/M/J/22 Q5 — rectification of AC voltage · 12 marks
• 9702/43/M/J/22 Q5 — rectification of AC voltage · 12 marks
• 9702/42/F/M/22 Q7 — AC to DC conversion · 6 marks
• 9702/41/O/N/21 Q9 — alternating voltage and electromagnetic induction · 9 marks
• 9702/42/O/N/21 Q5 — Modulation of radio waves · 8 marks
• 9702/43/O/N/21 Q9 — alternating voltage and electromagnetic induction · 9 marks
• 9702/42/M/J/21 Q10 — alternating current and r.m.s. value · 8 marks
• 9702/42/F/M/20 Q9 — AC circuits and transformers · 8 marks
• 9702/42/F/M/19 Q8 — Magnetic force on a current-carrying wire · 8 marks
• 9702/41/O/N/18 Q5 — digital vs analogue transmission · 8 marks
• 9702/42/O/N/18 Q10 — AC circuits and medical imaging · 9 marks
• 9702/43/O/N/18 Q5 — digital vs analogue transmission · 8 marks
• 9702/41/M/J/18 Q9 — force on a wire in magnetic field · 8 marks
• 9702/42/M/J/18 Q5 — radio communication and frequency modulation · 7 marks
• 9702/43/M/J/18 Q9 — force on a wire in a magnetic field · 8 marks
• 9702/42/F/M/18 Q3 — SHM, magnetic force, AC voltage, nuclear fission · 8 marks

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