CBSE Class 12 · Physics
Magnetism and Matter
Official NCERT chapter from Physics Part I–II (book code leph1). ExamMaster notes are original teaching at CBSE Class 12 depth.
This lesson follows the official chapter “Magnetism and Matter” in Physics Part I–II. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.
- CBSE Class 12
- Medium level
- 8 concepts
1The Bar Magnet
A bar magnet has two poles as taught; field lines leave north and enter south. A dipole moment m sits along the magnet. Cutting a magnet gives two smaller magnets, not a lone pole. Bar is the school magnet.
A lone north as a free pole is the leftover this heading refuses.
Figure. A bar has two poles. Magnetic moment m runs along the bar from S toward N. Field arrows here are straight stand-ins — the vocabulary has no arc.
How it works
- Name N and S and the line-mapThe bar.
- Keep m along the magnetThe moment.
- Refuse a single free poleThey come in pairs.
2Magnetism and Gauss’s Law
Magnetism and Gauss: flux of B through a closed surface is 0 as taught — no magnetic monopole. Gauss-for-B is a none-inside story, unlike Gauss-for-E. A closed surface around a magnet still has net 0.
Using q_m / ε0 as magnetic Gauss is a steal from E.
Figure. Gauss’s law for magnetism: net magnetic flux through any closed surface is zero. Flux in equals flux out. There is no isolated monopole to hide inside the box.
How it works
- Write net flux of B = 0The law.
- Say no monopole as the reasonThe why.
- Keep E-Gauss as a different writeTwo Gausses.
3Magnetisation and Magnetic Intensity
Magnetisation M and intensity H as taught: M is the material’s dipole-per-volume; H is the auxiliary field in the lesson’s write. B, H, M sit in a taught relation (B=μ0(H+M) as framed). These are material-words, not a bar-drawing.
Calling H the same as B always is a miss.
Figure. H is the applied magnetic intensity. M is the magnetisation the material adds. B in the material is built from both. Name each before you write B = μ0(H+M).
How it works
- Name M as the material-lookMagnetisation.
- Name H as the taught auxiliaryIntensity.
- Keep the B–H–M link as the lesson wrote itThe trio.
4Magnetic Properties of Materials
Magnetic materials: diamagnetic, paramagnetic, ferromagnetic as taught — weak oppose, weak along, strong along-and-stay. Soft iron versus steel if named. A type is a response-test, not a colour.
Calling every metal ferromagnetic is a steal.
Figure. Dia weakly opposes the field, para weakly follows it, ferro follows it strongly. Bar lengths are schematic — ferro susceptibility is orders of magnitude larger than the other two, so this is not a χ scale.
How it works
- Name the response (oppose / along / stay)The type.
- Keep ferromagnetism as the strong stayThe extra.
- Refuse shiny as the testA response.
5A definition is a test you can run
Magnetism-word is a test: a bar-dipole, flux 0, M/H, or a material-type. If you only say “north”, you have a heading.
A fridge-sticker is not the test.
Figure. A pole is a test, not a paint colour. Bring a compass: the needle’s south end faces the bar’s north end. If you cannot run that test, you have only named the bar.
How it works
- Name pole-pair, Gauss-B, or the typeThe object.
- Give the school sentenceThe test.
- Then the word has contentThe definition ran.
6Name the given before the unknown
The given is a bar or a material-name. The unknown is the type or the flux-claim. Copy “copper” before you treat it as iron.
Using ferromagnetic facts on a dia sample is a silent swap.
Figure. Name the givens on the bar before the unknown: each pole strength m, the pole separation 2l, then the moment M = m × 2l. Do not start from a slogan.
How it works
- Copy the object or the materialThe given.
- Name type or the Gauss-writeThe unknown.
- Then classifyGiven first.
7One worked case is enough at this class
One worked case is enough: a bar’s line-map, or “soft iron is a temporary magnet” as taught. Do not stack four hysteresis loops unless the lesson did.
A poster of ten fridge-magnets is not more science.
Figure. One school case: a dipole m in a uniform B. Torque is m B sinθ, largest when m is perpendicular to B, zero when they line up. Stay with that case.
How it works
- Take one bar or one typeThe case.
- Name poles or the responseThe teach.
- Stop — one caseThis class.
8A miss: swapping the school name for the picture
A miss: swapping the school name for a picture. “Diamagnetic” is a weak-oppose test — a pretty field-glow is a setting.
A fridge-photo without a type-word is a mute picture.
Figure. The school name “magnet” is not the figure. The figure is two poles you can test. Swapping the name for the picture is the miss this heading names.
How it works
- Keep the taught name (dia / para / ferro)The science.
- Use a picture only as a settingHonest.
- Refuse a swap of name for glowThe miss named.
Net flux of B through a closed surface is
- Zero as taught — no monopole
- q/ε0
- μ0 I
Gauss for B.
Notes
- Mapped to the official NCERT chapter “Magnetism and Matter”. Original teaching only — no textbook sentences.
- Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.
Formulas
- flux of B through a closed surface = 0
- B = μ0 (H+M) as taught
Recap
Hold these pegs from the official chapter “Magnetism and Matter”. The wording is ExamMaster’s teaching, not a textbook recap.
- The Bar Magnet
- A bar magnet has two poles as taught; field lines leave north and enter south.
- Magnetism and Gauss’s Law
- Magnetism and Gauss: flux of B through a closed surface is 0 as taught — no magnetic monopole.
- Magnetisation and Magnetic Intensity
- Magnetisation M and intensity H as taught: M is the material’s dipole-per-volume; H is the auxiliary field in the lesson’s write.
- Magnetic Properties of Materials
- Magnetic materials: diamagnetic, paramagnetic, ferromagnetic as taught — weak oppose, weak along, strong along-and-stay.
- A definition is a test you can run
- Magnetism-word is a test: a bar-dipole, flux 0, M/H, or a material-type.
- Name the given before the unknown
- The given is a bar or a material-name. The unknown is the type or the flux-claim. Copy “copper” before you treat it as iron.
Practise Magnetism and Matter
Reading is free and needs no account. Practice, mocks and progress live in the app.
- A 4-question practice set that ends the chapter
- 1 quick check with worked explanations
- Timed mocks scored with the real marking scheme
- Readiness tracked per topic, kept on your device