Simple A.C. Circuits: JAMB Physics Questions, Answers & Notes

What Simple A.C. Circuits covers in the JAMB Physics syllabus

Alternating current (a.c.) reverses direction periodically (mains is a.c., 50 Hz in Nigeria). Its peak value is the maximum; the r.m.s. value = peak/√2 and equals the d.c. that gives the same heating — quoted mains values (e.g. 240 V) are r.m.s. In a.c. circuits, a capacitor opposes current with capacitive reactance (Xc = 1/2πfC, falls with frequency) and an inductor with inductive reactance (XL = 2πfL, rises with frequency); their combination with resistance is impedance. At resonance XL = Xc and impedance is minimum. A rectifier converts a.c. to d.c.; a cathode-ray oscilloscope displays waveforms.

For Simple A.C. Circuits, JAMB expects you to be able to:

• Distinguish a.c. from d.c. and define peak and r.m.s. values
• Explain reactance, impedance and resonance in a.c. circuits
• Describe rectification, the CRO and mains supply values

Key facts & revision notes: Simple A.C. Circuits

These are the recurring points our Simple A.C. Circuits questions test — revise them until each feels automatic, then practise the questions above to lock them in.

• means alternating current — current that periodically reverses direction.
• periodically reverses direction, whereas d.c.
• flows in one direction only.
• Mains electricity is alternating current (a.c.).
• The peak (amplitude) is the maximum value the a.c.
• The root-mean-square value = peak value ÷ √2 (I_rms = I₀/√2).
• A capacitor's opposition to a.c.
• is its capacitive reactance (Xc).
• An inductor's opposition to a.c.
• is its inductive reactance (XL).
• Impedance (Z) is the total opposition to a.c., combining resistance and reactance.
• is the number of complete cycles per second (Hz).
• A rectifier (using diodes) converts a.c.
• A cathode-ray oscilloscope displays how a voltage varies with time (the waveform).
• At resonance XL = Xc, so they cancel and the impedance is minimum (just the resistance).
• Ideal capacitors and inductors store and return energy each cycle, dissipating no average power.
• The Nigerian mains supply has a frequency of 50 Hz.
• that would give the same average heating (power) in a resistor.
• Quoted mains voltages (e.g.
• A half-wave rectifier passes only one half of each a.c.
• V_rms = V₀/√2 = 311/1.414 ≈ 220 V.
• Inductive reactance XL = 2πfL increases with frequency.
• Capacitive reactance Xc = 1/(2πfC) decreases as frequency increases.
• A battery gives a steady, one-direction (d.c.) current.

Worked examples

Three Simple A.C. Circuits questions with the answer and a short explanation, so you can see how the topic is set before you practise the full set.

How Simple A.C. Circuits is tested in JAMB Physics

Our Simple A.C. Circuits bank holds 40 questions (6 easy, 17 medium, 17 hard). JAMB Physics typically returns to Simple A.C. Circuits year after year, so steady practice on this topic is high-value revision. Questions are multiple-choice with four options, and at UTME pace you get roughly 40 seconds each — which is why timed practice matters.

How to answer Simple A.C. Circuits questions

Work the stem first and predict the answer before you look at the options; then eliminate the ones that contradict the key facts above. Watch for “which is not…”, “all of the above” and “except” style stems, which are where rushed candidates lose easy marks on Simple A.C. Circuits. If a calculation or a precise definition is involved, work it from first principles rather than guessing from a half-remembered rule. When two options look right, re-read the stem for the qualifier that separates them — JAMB rarely repeats an option by accident. If you are still unsure, eliminate the two weakest choices to lift your odds, flag the question, and move on; never burn a full minute on one Physics item when the exam gives you about forty seconds each. Then come back to flagged questions with whatever time remains. The single most reliable way to get faster at Simple A.C. Circuits is repeated timed practice, so use the button above until the recurring patterns feel automatic.

Common mistakes to avoid in Simple A.C. Circuits

The errors that cost marks on Simple A.C. Circuits are usually careless rather than conceptual: misreading a negative stem, confusing two similar terms, or rushing a definition you actually know. Candidates also over-rely on “expo” and last-minute cramming instead of understanding the topic — which fails the moment JAMB rephrases a familiar idea. Treat every option as a claim to be checked against the facts above, keep your working tidy for any calculation, and don’t change a considered answer on a hunch. Above all, revise Simple A.C. Circuits actively by answering questions, not just by re-reading notes — recall under time is what the exam rewards.

Frequently asked questions

Is Simple A.C. Circuits part of the JAMB Physics syllabus?

Yes. Simple A.C. Circuits is a recognised topic in the JAMB Physics syllabus, covering distinguish a.c. from d.c. and define peak and r.m.s. values. You should be able to recall its key facts and apply them to multiple-choice questions.

How many Simple A.C. Circuits questions can I practise on Belmadeng?

There are 40 original, JAMB-standard Simple A.C. Circuits questions in our free bank, each with the correct answer and a worked explanation. You can practise them untimed or as a timed test.

What are the most important points to know about Simple A.C. Circuits?

Alternating current (a.c.) reverses direction periodically (mains is a.c., 50 Hz in Nigeria). Its peak value is the maximum; the r.m.s. value = peak/√2 and equals the d.c. that gives the same heating — quoted mains values (e.g. 240 V) are r.m.s. In a.c. circuits, a capacitor opposes current with cap…

How do I answer Simple A.C. Circuits questions quickly in JAMB?

Read the stem carefully, eliminate clearly wrong options, and match the remaining choices to the key facts for Simple A.C. Circuits. Practising timed Simple A.C. Circuits questions builds the speed you need for UTME's pace of about 40 seconds per question.

Are these JAMB Physics Simple A.C. Circuits questions past questions or original?

They are original questions written to JAMB (UTME) standard and mapped to the official syllabus — not reproduced past papers. This keeps them legal to use freely while closely mirroring how the real exam tests the topic.

Where can I practise Simple A.C. Circuits questions free without signing up?

Right here — tap “Start Simple A.C. Circuits practice” on this page to begin instantly. Belmadeng's CBT practice is completely free and needs no sign-up, download or subscription.

About these questions: original, JAMB-standard items written from the official UTME Physics syllabus (last reviewed 2026-09-18). Belmadeng is an independent study platform and is not affiliated with JAMB. Spotted an error? Use the report link.