MHT-CET Physics · Teaching notes
Magnetic Materials — MHT-CET Physics
Magnetic Materials has 33 past-year questions in the MHT-CET bank and only one is HARD. It is mostly definitions and one-line relations: a magnet's dipole moment and what cutting or bending it does, the orbital moment of an electron, how B, H and the magnetisation M are linked through the susceptibility, and how dia-, para- and ferromagnets differ — including hysteresis and shielding. Every PYQ is tagged.
Every subtopic, worked example, formula and trap in one printable document — answers shown, ready to share.
Subtopic notes
Magnetic Dipole Moment
10 PYQsA magnet's dipole moment is its pole strength times its length (or magnetisation times volume); in a field B it feels a torque MB sin θ, stores energy −MB cos θ and oscillates with period 2π√(I/MB); an orbiting electron has a moment proportional to its angular momentum, e/2m times L.
Magnetisation, Susceptibility and Permeability
13 PYQsInside a material the field is B = μ₀(H + M), where H is set by the currents and M, the magnetisation, is the material's own dipole moment per unit volume; M = χH defines the susceptibility, so B = μ₀(1 + χ)H and the relative permeability is μᵣ = 1 + χ.
Dia-, Para- and Ferromagnets, Hysteresis and Shielding
10 PYQsDiamagnets have a small negative susceptibility that does not depend on temperature, paramagnets a small positive one that falls as 1/T (Curie's law), and ferromagnets a huge one that disappears above the Curie temperature; only ferromagnets show hysteresis, and soft ferromagnets are used for shielding and electromagnets.
Formula & revision sheet
4 formulas · 2 reference tables · 12 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
4 formulas · 2 reference tables · 12 gotchas across all subtopics — the exam-eve cheat-sheet
Formulas (2)
Watch out for (4)
- Keeping the length when a rod is bent→ Moment, Torque, Work and Oscillation
- Subtracting moments of magnets held with like poles together→ Moment, Torque, Work and Oscillation
- Writing the gyromagnetic ratio as e/m→ The Orbiting Electron's Moment
- Dropping the minus sign→ The Orbiting Electron's Moment
Watch out for (4)
- Taking μᵣ = χ→ B, H, M, χ and μ
- Quoting (1 + χ) as the percentage rise→ B, H, M, χ and μ
- Leaving cm² and cm in the volume→ Computing a Magnetisation
- Using μᵣ where μᵣ − 1 belongs→ Computing a Magnetisation
Reference tables (2)
The Three Classes and Curie's Law3 rows
| Class | Susceptibility | Temperature |
|---|---|---|
| Diamagnetic | Small, negative | Independent of T |
| Paramagnetic | Small, positive | χ = C/T (Curie's law) |
| Ferromagnetic | Very large, positive | Becomes paramagnetic above the Curie temperature |
Hysteresis, Electromagnets and Shielding3 rows
| Use | Retentivity | Coercivity |
|---|---|---|
| Electromagnet core (soft iron) | High | Low |
| Permanent magnet (steel, alnico) | High | High |
| Magnetic shield | — | Soft ferromagnet, high permeability |
Watch out for (4)
- Letting a diamagnet's χ change with temperature→ The Three Classes and Curie's Law
- Writing Curie's law upside down→ The Three Classes and Curie's Law
- Swapping retentivity and coercivity on the loop→ Hysteresis, Electromagnets and Shielding
- Shielding with a diamagnet→ Hysteresis, Electromagnets and Shielding
PYQ weightage by concept
6 concepts · 33 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
6 concepts · 33 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Moment, Torque, Work and Oscillation | 7 | 21% |
| The Orbiting Electron's Moment | 3 | 9% |
| Concept | PYQs | Share |
|---|---|---|
| B, H, M, χ and μ | 9 | 27% |
| Computing a Magnetisation | 4 | 12% |
| Concept | PYQs | Share |
|---|---|---|
| Hysteresis, Electromagnets and Shielding | 6 | 18% |
| The Three Classes and Curie's Law | 4 | 12% |
Test yourself on Magnetic Materials
15 past MHT-CET questions from this chapter, timed at 14 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.