Everything you need for this topic on one page: the ideas, the formulas, the traps, and free lectures that explain it well.
Last updated: 26 October 2026
AC voltage and current, RMS values, reactance, impedance, phasors, resonance, power factor and transformers.
Printable Alternating Current formula sheet: formulas, key ideas and traps on one page. Save it as a PDF for offline revision.
Appears frequently. Draw a phasor diagram for every RLC question. It avoids almost all sign mistakes.
Prerequisites: Electromagnetic Induction.
Chapter names follow the current rationalised NCERT textbooks. Read these sections before solving PYQs.
| Class | Book | Chapter | Sections JEE asks from |
|---|---|---|---|
| Class 12 | Physics Part I | Alternating Current | AC Voltage Applied to a Series LCR Circuit; Resonance; Power in AC Circuit: The Power Factor; Transformers; AC Voltage Applied to an Inductor |
Question. A series LCR circuit has L = 0.4 H, C = 100 μF, and R = 30 Ω connected to a 200 V (RMS) AC source with variable frequency. (a) Find the resonant angular frequency. (b) At resonance, find the RMS current and voltage across the inductor. (c) Calculate the quality factor Q. (d) When the angular frequency is changed to 100 rad/s, find the impedance, current, power factor, and average power dissipated.
Answer: (a) ω₀ = 158 rad/s (b) I₀ = 6.67 A, V_L = 421 V (c) Q = 2.1 (d) Z = 67.1 Ω, I = 2.98 A, cos φ = 0.447, P = 266 W
This example was solved twice independently and both solutions agree.
Full-chapter free lectures picked from YouTube search results by views, from established JEE channels (mostly in Hinglish). Use the subtopic list to jump straight to the part you need (timestamps come from each video's own chapter list). Watch one, then solve PYQs the same day.
Appears frequently. It is part of the official 'Electromagnetic Induction and Alternating Currents' unit in the JEE Main 2027 syllabus.
V_rms = V₀/√2; X_L = ωL, X_C = 1/ωC, Z = √(R² + (X_L − X_C)²); Resonance ω₀ = 1/√(LC); Q = ω₀L/R.
Understand the key ideas from NCERT or one full lecture, learn the formula sheet, then solve 25–30 past JEE questions on the topic. Draw a phasor diagram for every RLC question. It avoids almost all sign mistakes.
