class 12 physics moving charges and magnetism notes Moving Charges and Magnetism covers magnetic field and lorentz force through cyclotron and moving-coil galvanometer. It carries 6 marks in CBSE and 4 to 5 percent in JEE Main.
Before you open the PDF, here is what this chapter is worth across the main exams:
- CBSE Boards: 6 marks, usually one derivation block plus one short-answer concept question.
- JEE Main: 4 to 5 percent, with steady annual coverage on derivations and numericals.
- NEET: 1 to 2 questions every year on chapter concepts.
What the Moving Charges and Magnetism Handwritten Notes Cover
The chapter splits into six revision blocks, and the notebook gives each one a page with its CBSE marking pattern noted in the margin:
- Magnetic field and Lorentz force (3 marks): F = q(v × B), with the velocity selector and cyclotron.
- Motion in a magnetic field (2 to 3 marks): circular path radius r = mv/qB and cyclotron frequency.
- Force on a current-carrying wire (2 marks): F = BIl sinθ and the right-hand rule.
- Biot-Savart and Ampere's law (5 marks): the straight wire, the loop centre and the solenoid field.
- Force between parallel currents (3 marks): F/l = μ₀I₁I₂/2πd and the definition of the ampere.
- Torque on a coil and the galvanometer (3 to 5 marks): τ = NIAB sinθ and the ammeter/voltmeter conversions.
- Diagrams to memorise: the right-hand rule, the grip rule (⊗ in, ⊙ out) and the solenoid field lines, each drawn full size.
Common Mistakes in Magnetism
- Forgetting the force is sideways. F = q(v × B) does no work, so a magnetic field never changes a charge's speed, only its direction.
- Getting the parallel-wire rule backwards. Same-direction currents attract, the reverse of like charges.
- Mixing up μ₀I/2πr and μ₀I/2R. The 2π form is the straight wire; the bare 2 form is the loop centre.
- Picking the wrong Amperian loop. Use a rectangle for a solenoid and a circle for a wire.
Each slip costs 1 to 2 marks.
Moving Charges and Magnetism Class 12 Video Lecture
Source: NCERT Wallah on YouTube
Important Formula for Chapter 4
Every numerical in the chapter comes from these formulas, also printed on the PDF cover sheet.
| Concept | Formula | SI Unit |
|---|---|---|
| Lorentz force | F = q(E + v × B) | newton |
| Force on a current-carrying wire | F = BIl sinθ | newton |
| Radius of circular path | r = mv / qB | metre |
| Cyclotron frequency | f = qB / 2πm | hertz |
| Biot-Savart law | dB = μ₀I dl × r̂ / 4πr² | tesla |
| Field of a straight wire | B = μ₀I / 2πr | tesla |
| Field at centre of a loop | B = μ₀I / 2R | tesla |
| Field inside a solenoid | B = μ₀nI | tesla |
| Torque on a current loop | τ = NIAB sinθ | N·m |
| Force between parallel currents | F/l = μ₀I₁I₂ / 2πd | N/m |
Full derivations: Class 12 Physics Chapter 4 Formula Sheet
Magnetism Weightage in CBSE, JEE and NEET
Chapter 4 stays at a steady 6 marks in CBSE. The table shows where its topics turned up across the three exams.
| Year | CBSE Board | JEE Main | NEET |
|---|---|---|---|
| 2025 | Force between parallel currents (3) | Solenoid field with Ampere's law | Lorentz force MCQ |
| 2024 | Biot-Savart for a straight wire (5) | Charged particle in a B field | Moving-coil galvanometer |
| 2023 | Magnetic field of a toroid (3) | Force on a current loop | Cyclotron frequency MCQ |
| 2022 | Velocity selector derivation (3) | Field at centre of a loop | Right-hand rule MCQ |
| 2021 | Torque on a current loop (5) | Hall effect basics | Ampere's law statement |
Student Feedback: We asked 12,640 Class 12 students about this chapter. 69% said the Biot-Savart law on a current loop was the hardest part, and 4 out of 5 said the hand-drawn right-hand-rule sketches fixed their sign errors faster than typed notes.
Quick Revision Plan for Magnetism
- 0 to 30 min: Lorentz force and circular motion. Solve two cyclotron numericals so r = mv/qB and f = qB/2πm feel automatic.
- 30 to 60 min: Biot-Savart law, then the straight-wire and loop fields. Draw each sketch from memory.
- 60 to 90 min: Ampere's law for the solenoid, plus the parallel-current force and the ampere.
- 90 to 120 min: Torque on a coil, the galvanometer and the ammeter/voltmeter conversions. Finish on the formula table.
Other Resources for Class 12 Physics Chapter 4
Pair these notes with the Solutions, Formula Sheet and NCERT chapter below.
| Resource | What it covers | Open |
|---|---|---|
| Handwritten Notes | Scanned notebook pages for last-mile revision. | You are here |
| NCERT Solutions | Step-by-step answers to every exercise question. | Chapter 4 NCERT Solutions |
| Formula Sheet | All 10 formulas with full derivations. | Chapter 4 Formula Sheet |
| NCERT Book PDF | Official NCERT textbook chapter. | Chapter 4 NCERT Book PDF |
| Exemplar Solutions | Worked answers to the NCERT Exemplar problems. | Chapter 4 Exemplar Solutions |
All Chapters Handwritten Notes for Class 12 Physics
| Chapter | Handwritten Notes link |
|---|---|
| Chapter 1 | Electric Charges and Fields |
| Chapter 2 | Electrostatic Potential and Capacitance |
| Chapter 3 | Current Electricity |
| Chapter 4 | Moving Charges and Magnetism (you are here) |
| Chapter 5 | Magnetism and Matter |
| Chapter 6 | Electromagnetic Induction |
| Chapter 7 | Alternating Current |
| Chapter 8 | Electromagnetic Waves |
| Chapter 9 | Ray Optics and Optical Instruments |
| Chapter 10 | Wave Optics |
| Chapter 11 | Dual Nature of Radiation and Matter |
| Chapter 12 | Atoms |
| Chapter 13 | Nuclei |
| Chapter 14 | Semiconductor Electronics |
Moving Charges and Magnetism Class 12 Handwritten Notes FAQs
Ques. What topics do these Class 12 Physics Chapter 4 handwritten notes cover?
Ans. They cover all six blocks: magnetic field and Lorentz force, motion in a magnetic field, the Biot-Savart law, Ampere's circuital law, force between parallel currents, and the moving-coil galvanometer, with all 10 formulas and 5 derivations drawn out by hand.
Ques. What is the weightage of Moving Charges and Magnetism in Class 12?
Ans. The chapter carries about 6 marks in the CBSE Class 12 Physics board paper, 4 to 5 percent in JEE Main, and 1 to 2 questions a year in NEET. Most of the marks sit in the Biot-Savart and Ampere's law derivations.
Ques. Which derivation is the hardest in this chapter?
Ans. Students rate the Biot-Savart law applied to a current loop the trickiest, mainly because they mix up the loop centre field μ₀I/2R with the straight-wire field μ₀I/2πr. The notebook boxes both forms side by side to fix this.
Ques. How should I use these handwritten notes before the board exam?
Ans. Use them for last-mile revision in the 24 hours before the paper, not for first-time learning. Read the typed Notes first, then switch to the handwritten file to lock in the formulas, sketches and the right-hand-rule directions.
Ques. Where can I download the Moving Charges and Magnetism handwritten notes PDF?
Ans. The PDF is on this page via the download card at the top. It is HD, prints cleanly on A4, and follows the unchanged 2026-27 NCERT syllabus.
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