Class 12 Physics Chapter 7 Alternating Current covers AC circuits, LCR resonance, power factor, and transformers. The chapter carries 6 marks in CBSE and appears in JEE Main every year. This page hosts the Alternating Current Formula Sheet PDF for quick revision.
- 6 marks in CBSE from this chapter, tested through derivations and numericals every year without fail.
- 3-4% weightage in JEE Main: LCR resonance, Q-factor, and transformer problems come every session.
- 2-3 NEET questions per year on reactance, phasor diagrams, and AC generator EMF.
Class 12 Physics Chapter 7 Formula Sheet: Complete Reference
The 10 formulas below cover every numerical in Alternating Current. Each row gives the concept, the formula, and the SI unit.
This formula sheet is calibrated for both CBSE Boards and JEE Main. Foundational formulas cover 1-mark MCQs. Derived formulas cover 5-mark numericals. NEET students should focus on the first five rows plus dimensional reasoning.
| Concept | Formula | SI Unit |
|---|---|---|
| Instantaneous voltage | V = V_0 sin(omega t) | volt |
| RMS value | I_rms = I_0 / sqrt(2) | ampere |
| Inductive reactance | X_L = omega L = 2 pi f L | ohm |
| Capacitive reactance | X_C = 1 / (omega C) | ohm |
| Impedance (LCR) | Z = sqrt(R^2 + (X_L - X_C)^2) | ohm |
| Resonance frequency | f_r = 1 / (2 pi sqrt(L C)) | Hz |
| Power factor | cos phi = R / Z | n/a |
| Average power | P_avg = V_rms I_rms cos phi | watt |
| Quality factor | Q = omega_r L / R | n/a |
| Transformer turns ratio | V_s / V_p = N_s / N_p | n/a |
AC quick numbers: mains, RMS, resonance.
Alternating Current Video Lecture: Class 12 Physics Chapter 7
Source: JEE Wallah on YouTube
Series LCR resonance: at resonance frequency the circuit becomes purely resistive.
Physics Class 12 Chapter 7 Formula Sheet: Topic-by-Topic Breakdown
The chapter splits into 6 topic blocks. Each block has its own key formulas and exam mark allocation:
- AC voltage applied to a resistor: 1-mark on V and I in phase
- Phasor representation: 2-mark conceptual question
- AC through inductor and capacitor: 3-mark on reactance
- LCR series circuit and resonance: 5-mark on Z and resonance frequency
- Power in AC circuit and power factor: 3-mark on P = V_rms I_rms cos phi
- Transformer and AC generator: 3-mark on turns ratio and EMF derivation
How to Use This Class 12 Physics Chapter 7 Formula Sheet
Students get the most from this formula sheet when they use it in three ways:
- Night-before revision: scan all 10 formula rows. Check you can state each without notes.
- During practice sessions: keep the PDF open in a second tab for quick formula lookup.
- For 5-mark derivations: formulas that appear in CBSE board derivations are flagged in the PDF. Work through each derivation using the formula as the starting point.
Alternating Current Weightage Compared Across Class 12 Physics Chapters
The table below shows CBSE board average marks for each chapter over the last five papers.
| Chapter | Topic | Avg CBSE Marks |
|---|---|---|
| Ch 1 | Electric Charges and Fields | 6 marks |
| Ch 2 | Electrostatic Potential and Capacitance | 7 marks |
| Ch 3 | Current Electricity | 7 marks |
| Ch 4 | Moving Charges and Magnetism | 6 marks |
| Ch 5 | Magnetism and Matter | 3 marks |
| Ch 6 | Electromagnetic Induction | 5 marks |
| Ch 7 | Alternating Current | 6 marks |
| Ch 8 | Electromagnetic Waves | 2 marks |
| Ch 9 | Ray Optics and Optical Instruments | 7 marks |
| Ch 10 | Wave Optics | 5 marks |
| Ch 11 | Dual Nature of Radiation and Matter | 4 marks |
| Ch 12 | Atoms | 3 marks |
| Ch 13 | Nuclei | 3 marks |
| Ch 14 | Semiconductor Electronics | 6 marks |
Alternating Current Previous Year Questions Weightage (2021 to 2026)
The table maps CBSE Board, JEE Main, and NEET appearances of Chapter 7 topics over the last six sessions.
| Year | CBSE Board | JEE Main | NEET |
|---|---|---|---|
| 2026 | AC generator derivation (5 marks) | LCR resonance frequency (4 marks) | LCR circuit, resonance and power factor (2 questions) |
| 2025 | LCR series circuit and power factor (5 marks) | RMS value and peak value relation | Reactance comparison MCQ |
| 2024 | Transformer step-up problem (3 marks) | Q-factor of LCR circuit | RMS value derivation |
| 2023 | Power factor and wattless current (3 marks) | Resonance angular frequency | Phasor diagram MCQ |
| 2022 | AC through inductor derivation (3 marks) | Transformer efficiency | LC oscillation period |
| 2021 | - | Power dissipation in LCR | AC generator EMF |
Common Mistakes in Alternating Current: Class 12 Physics Chapter 7
Mistake 1: Substituting values before simplifying the formula. Always isolate the unknown first, then substitute.
Mistake 2: Forgetting unit conversion. Use SI units everywhere unless the question says otherwise.
Mistake 3: Using approximate constants for 5-mark numericals. Use the exact value given in the question paper.
Mistake 4: Confusing similar-looking formulas, for example series LCR impedance versus parallel capacitor formulas. The Quick-Reference Table above separates them clearly.
Each mistake costs 1 to 2 marks.
Student Feedback
In a Collegedunia poll of 13,980 Class 12 Physics students before the 2026 boards:
- 74% of students put the formula sheet at the top of their revision list.
- 58% reviewed the formula sheet daily in the 7 days before the boards.
- 4 out of 5 students kept a printed copy in their notebook.
- Average revision time: 12 minutes per chapter for a focused pass.
- 67% of students used the formula sheet together with the Chapter Notes during night-before revision.
Source: 2025-26 Class 12 Physics student poll. Sample of 13,980 students from CBSE schools across 16 states.
Formula Sheet for Three Exam Tracks: CBSE, JEE Main, NEET
Students preparing for different exams use this formula sheet differently:
- CBSE Boards: foundational and middle formulas cover 95% of board questions. Focus on rows 1-7.
- JEE Main: the full table plus 2-3 appendix extensions are essential. Pay attention to Q-factor and power dissipation.
- NEET: foundational rows, dimensional reasoning, and careful unit checks. Focus on rows 1-5.
Other Resources for Class 12 Alternating Current
| Resource | Link |
|---|---|
| Notes | Class 12 Alternating Current Notes |
| Solutions | Class 12 Alternating Current NCERT Solutions |
| NCERT Book PDF | Class 12 Alternating Current NCERT Book PDF |
| Exemplar Book PDF | Class 12 Alternating Current NCERT Exemplar Book PDF |
| Exemplar Solutions | Class 12 Alternating Current NCERT Exemplar Solutions |
| Handwritten Notes | Class 12 Alternating Current Handwritten Notes |
| Formula Sheet | Alternating Current Formula Sheet |
NCERT Formula Sheets for Class 12 Physics: All Chapters
| Chapter | Resource |
|---|---|
| Chapter 1 | Electric Charges and Fields Formula Sheet |
| Chapter 2 | Electrostatic Potential and Capacitance Formula Sheet |
| Chapter 3 | Current Electricity Formula Sheet |
| Chapter 4 | Moving Charges and Magnetism Formula Sheet |
| Chapter 5 | Magnetism and Matter Formula Sheet |
| Chapter 6 | Electromagnetic Induction Formula Sheet |
| Chapter 7 | Alternating Current Formula Sheet |
| Chapter 8 | Electromagnetic Waves Formula Sheet |
| Chapter 9 | Ray Optics and Optical Instruments Formula Sheet |
| Chapter 10 | Wave Optics Formula Sheet |
| Chapter 11 | Dual Nature of Radiation and Matter Formula Sheet |
| Chapter 12 | Atoms Formula Sheet |
| Chapter 13 | Nuclei Formula Sheet |
| Chapter 14 | Semiconductor Electronics Formula Sheet |
Class 12 Physics Chapter 7 Alternating Current Formula Sheet FAQs
Ques. How many formulas are in the Class 12 Chapter 7 Physics formula sheet?
Ans. 10 formulas cover every numerical the chapter generates. The Quick-Reference Table above lists them with SI units. The PDF carries the same list on a single A4 cover sheet for night-before revision.
Ques. What is the weightage of Class 12 Physics Chapter 7?
Ans. Chapter 7 carries 6 marks in CBSE Class 12 Physics, 3 to 4 percent in JEE Main, and 2 to 3 questions per year in NEET. The formula sheet covers the formulas for every variant.
Ques. Where can I download the Class 12 Physics Chapter 7 formula sheet PDF?
Ans. The formula sheet PDF is available directly on this page via the flipbook above. It includes all 10 formulas plus JEE and NEET extensions on a single A4 page.
Ques. Are the JEE Main extensions covered in this formula sheet?
Ans. Yes. The formula sheet includes 2-3 extensions that JEE Main and JEE Advanced test but CBSE rarely asks. These are flagged with a distinct marker in the PDF.
Ques. What is the most-asked formula in Alternating Current?
Ans. Instantaneous voltage is the foundational formula and appears in most Chapter 7 numericals. The full list of high-frequency formulas is in the Quick-Reference Table above.
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