The Class 12 Physics Chapter 4 Moving Charges and Magnetism notes give you a quick, exam-ready revision of the whole chapter. They cover the magnetic field, the Lorentz force, the Biot-Savart law, Ampere's law, the cyclotron, and the moving-coil galvanometer. You can read and download the full notes PDF right here on this page.
Here is what Class 12 Physics Chapter 4 is worth across the main exams:
- CBSE Boards: 6 marks, usually one derivation plus one short concept question.
- JEE Main: 4 to 5 percent, with steady cover on derivations and numericals.
- NEET: 1 to 2 questions every year on chapter concepts.
Also Check:
- Class 12 Moving Charges and Magnetism NCERT Solutions
- Class 12 Moving Charges and Magnetism Formula Sheet
Topic-by-Topic Summary of Class 12 Physics Chapter 4 Moving Charges and Magnetism
The chapter splits into 6 sub-topic blocks. Each block below is mapped to its usual CBSE marking pattern.
- Magnetic field and Lorentz force: 2-mark on F = q(v cross B) and F = IL cross B.
- Biot-Savart law: 3-mark derivation of the field due to a current element.
- Straight wire and circular loop: 5-mark derivation of the magnetic field.
- Ampere's circuital law: 3-mark numerical on the field of a solenoid or toroid.
- Force between parallel currents: 2-mark on F/L = mu_0 I_1 I_2 / (2 pi d).
- Cyclotron and galvanometer: 3-mark on r = mv/qB and meter conversion.
Moving Charges and Magnetism Video Lecture for Class 12 Physics
Source: Magnet Brains on YouTube
The formula chart below sums up every relation you need for numericals in this chapter.
Lorentz force: the combined electric and magnetic action on a charge.
All Formulas in Class 12 Physics Chapter 4 Moving Charges and Magnetism
The table below lists every formula the chapter uses for numericals. The same list sits on the back page of the notes PDF for last-minute revision.
| Concept | Formula | SI Unit |
|---|---|---|
| Lorentz force | F = q (E + v cross B) | newton |
| Force on current-carrying wire | F = I L cross B | newton |
| Biot-Savart law | dB = (mu_0 / 4 pi) I dL cross r_hat / r squared | tesla |
| Field of infinite straight wire | B = mu_0 I / (2 pi d) | tesla |
| Field at centre of circular loop | B = mu_0 I / (2 R) | tesla |
| Field on axis of circular loop | B = mu_0 I R² / (2 (R² + x²)^(3/2)) | tesla |
| Ampere's law | closed integral B . dL = mu_0 I_enc | n/a |
| Solenoid (long) | B = mu_0 n I | tesla |
| Cyclotron radius | r = m v / (q B) | metre |
| Cyclotron frequency | f = q B / (2 pi m) | hertz |
Full formula sheet with derivations: Class 12 Moving Charges and Magnetism Formula Sheet
Key Derivations in Class 12 Physics Chapter 4 Moving Charges and Magnetism
These 5 derivations carry most of the marks in the chapter. Each one in the notes PDF shows the full geometry sketch, the integral set-up, and the boundary conditions.
| Derivation | Marks (CBSE) |
|---|---|
| Biot-Savart law (basic form) | 3 |
| Field due to a straight current-carrying wire | 5 |
| Field at centre and on axis of a circular loop | 5 |
| Force between two parallel currents | 3 |
| Cyclotron working principle | 3 |
Moving Charges and Magnetism Weightage Across Class 12 Physics Chapters
The table below shows how Class 12 Physics Chapter 4 weightage compares with the other chapters. Marks are CBSE board averages 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 |
Moving Charges and Magnetism Previous Year Questions (2021 to 2026)
The table below maps how Class 12 Physics Chapter 4 topics showed up in CBSE Board, JEE Main, and NEET over the last six sessions.
| Year | CBSE Board | JEE Main | NEET |
|---|---|---|---|
| 2026 | Field on axis of circular loop (5 marks) | Cyclotron radius numerical (4 marks) | Force on a moving charge and field of a current (2 questions) |
| 2025 | Force between parallel currents (3 marks) | Solenoid field with Ampere's law | Lorentz force MCQ |
| 2024 | Biot-Savart applied to straight wire (5 marks) | Charged particle in B field | Moving-coil galvanometer |
| 2023 | Magnetic field of toroid (3 marks) | Force on current-carrying loop | Cyclotron frequency MCQ |
| 2022 | Velocity selector derivation (3 marks) | Field at centre of loop | Right-hand rule MCQ |
| 2021 | - | Hall effect basics | Ampere's law statement |
Common Mistakes in Moving Charges and Magnetism
Mistake 1: Skipping the unit balance step. CBSE markers give marks for showing dimensional consistency on derivations.
Mistake 2: Mixing scalar and vector quantities. Add scalars by value and vectors by their components.
Mistake 3: Forgetting boundary conditions in the straight wire and circular loop derivation. State your assumptions before the algebra.
Mistake 4: Putting in numbers too early. Boards mark down for premature numerical substitution, so keep it symbolic till the last step.
Each one costs 1 to 2 marks.
Students rated this chapter in a Collegedunia poll. Here is what they told us.
Student Feedback
- 69% of students found Biot-Savart law applied to current loops the most confusing sub-topic.
- 57% said the cyclotron motion derivation tripped them up on at least one class test.
- 4 out of 5 students revised the Biot-Savart law the night before boards.
- Average time was 5 hours for first read and 2.4 hours for focused revision.
- 61% of students read these notes at least twice before their boards.
Source: 2025-26 Class 12 Physics student poll, 12,640 students from CBSE schools across 16 states.
Use the 2-hour plan below for a fast final pass before the exam.
FBV right-hand rule: how to find the Lorentz force direction.
How to Revise Class 12 Physics Chapter 4 Moving Charges and Magnetism in 2 Hours
- 0 to 30 min: Magnetic field and Lorentz force, plus Biot-Savart law. Solve 2 numericals.
- 30 to 60 min: Straight wire and circular loop derivation walkthrough.
- 60 to 90 min: Force between parallel currents block.
- 90 to 120 min: Run through the 10-formula table and the 5-derivation index.
Give yourself 5 to 6 hours for the first read. These notes work best once you have done Current Electricity.
Other Resources for Class 12 Physics Chapter 4 Moving Charges and Magnetism
| Resource | Link |
|---|---|
| NCERT Solutions | Moving Charges and Magnetism Solutions |
| Formula Sheet | Moving Charges and Magnetism Formula Sheet |
| NCERT Book PDF | Moving Charges and Magnetism Book PDF |
| Exemplar Book PDF | Moving Charges and Magnetism Exemplar Book PDF |
| Exemplar Solutions | Moving Charges and Magnetism Exemplar Solutions |
| Handwritten Notes | Moving Charges and Magnetism Handwritten Notes |
| Notes | Moving Charges and Magnetism Notes |
NCERT Notes for Class 12 Physics: All Chapters
| Chapter | Resource |
|---|---|
| Chapter 1 | Electric Charges and Fields Notes |
| Chapter 2 | Electrostatic Potential and Capacitance Notes |
| Chapter 3 | Current Electricity Notes |
| Chapter 4 | Moving Charges and Magnetism Notes |
| Chapter 5 | Magnetism and Matter Notes |
| Chapter 6 | Electromagnetic Induction Notes |
| Chapter 7 | Alternating Current Notes |
| Chapter 8 | Electromagnetic Waves Notes |
| Chapter 9 | Ray Optics and Optical Instruments Notes |
| Chapter 10 | Wave Optics Notes |
| Chapter 11 | Dual Nature of Radiation and Matter Notes |
| Chapter 12 | Atoms Notes |
| Chapter 13 | Nuclei Notes |
| Chapter 14 | Semiconductor Electronics Notes |
Class 12 Physics Chapter 4 Moving Charges and Magnetism Notes FAQs
Ques. What are the main topics in Class 12 Physics Chapter 4 notes?
Ans. The notes cover the magnetic field and Lorentz force, the Biot-Savart law, the field of a straight wire and circular loop, Ampere's circuital law, force between parallel currents, and the cyclotron and moving-coil galvanometer.
Ques. What are the most-asked derivations in this chapter?
Ans. Five derivations carry most of the marks: Biot-Savart law, field due to a straight wire, field at the centre and on the axis of a circular loop, force between parallel currents, and the cyclotron principle.
Ques. How many formulas are in the Class 12 Physics Chapter 4 notes?
Ans. Ten formulas cover every numerical the chapter generates. The table above lists them with their SI units, and the notes PDF carries the same list on one cover sheet.
Ques. What is the weightage of Class 12 Physics Chapter 4?
Ans. Chapter 4 carries 6 marks in CBSE Class 12 Physics, 4 to 5 percent in JEE Main, and 1 to 2 questions per year in NEET.
Ques. Where can I download the Class 12 Physics Chapter 4 notes PDF?
Ans. You can read and download the notes PDF directly from the card at the top of this page. It covers all 10 formulas, 5 derivations, and worked numericals.
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