Last Updated: May 2026
JEE Main Magnetism and Matter 2027 — Class XII Physics Chapter 5 — typically yields 1-2 questions per JEE Main session, often combined with electromagnetism. The chapter is high-yield because it overlaps with magnetic field due to current (Chapter 4) and electromagnetic induction (Chapter 6). This guide consolidates the key formulae, dia/para/ferro classifications, hysteresis loop, earth’s magnetism, and 35 practice MCQs.
Quick Facts: JEE Magnetism & Matter 2027
| Aspect | Detail |
|---|---|
| NCERT chapter | Class XII Physics, Chapter 5 |
| Average JEE Main questions | 1-2 |
| Difficulty | Easy-Moderate |
| High-yield zones | Magnetisation, susceptibility, hysteresis, earth’s magnetism |
| Trap zone | χ vs μr sign for dia/para/ferro |
Magnetic Dipole and Bar Magnet
- Magnetic moment M = m × 2L (m = pole strength, 2L = magnet length); SI unit: A·m².
- Torque on dipole in field: τ = M × B; magnitude τ = MB sin θ.
- Potential energy: U = −M·B; minimum when M ∥ B (stable), maximum when M anti-parallel (unstable).
Field Due to a Bar Magnet
| Position | Field B |
|---|---|
| Axial (end-on) | μ₀(2M)/(4πr³) — short magnet |
| Equatorial (broadside-on) | μ₀M/(4πr³) — short magnet |
Memory tip: Axial = 2× Equatorial; analogous to electric dipole.
Magnetisation, Magnetic Intensity and Susceptibility
- Magnetisation (M): Net magnetic moment per unit volume.
- Magnetic intensity (H): related to free current density.
- Magnetic susceptibility (χ): M = χH.
- Permeability (μ) and relative permeability (μr): μ = μ₀(1 + χ); μr = 1 + χ.
- B = μ₀(H + M).
Classification of Magnetic Materials
| Type | χ (susceptibility) | μr | Behaviour | Example |
|---|---|---|---|---|
| Diamagnetic | Small, negative | < 1 | Repelled by magnet | Bi, Cu, Au, water, NaCl |
| Paramagnetic | Small, positive | Slightly > 1 | Weakly attracted | Al, Pt, Mn, O₂ |
| Ferromagnetic | Large, positive | ≫ 1 | Strongly attracted, retains magnetisation | Fe, Co, Ni, Gd, alnico |
Curie Law and Curie Temperature
- Curie Law (paramagnetic): χ = C/T (inversely proportional to absolute temperature).
- Curie temperature (TC): Above this, ferromagnet → paramagnet (Fe: 770 °C, Co: 1131 °C, Ni: 358 °C).
- Below TC: domains aligned; above TC: thermal randomisation dominates.
Hysteresis Loop
- Retentivity (Br): Magnetisation left when H = 0.
- Coercivity (Hc): Reverse field needed to demagnetise.
- Soft magnets (low coercivity): Soft iron — used in transformer cores.
- Hard magnets (high coercivity): Steel, alnico — used in permanent magnets.
- Area enclosed = energy lost per cycle (heat).
Earth’s Magnetism (NEET-NCERT Crossover)
- Earth behaves like a giant bar magnet with magnetic south pole near geographic north.
- Three elements: Magnetic declination (θ), magnetic dip / inclination (δ), horizontal component (H).
- BH = B cos δ; BV = B sin δ; tan δ = BV/BH.
- Magnetic equator: dip = 0°; magnetic poles: dip = 90°.
Common JEE Trap Zones
- χ vs μr sign for diamagnetic — χ < 0 but μr < 1.
- Bohr magneton (μB) = 9.27 × 10⁻²⁴ A·m² — appears in atomic magnetism MCQs.
- Curie law applies only to paramagnets, not diamagnets.
- Soft iron has high permeability but LOW retentivity → preferred for transformer cores.
- Vibration magnetometer formula: T = 2π √(I/MBH).
FAQ — JEE Magnetism & Matter 2027
Q1. Why is soft iron used in electromagnets and not steel?
Soft iron has high permeability and low retentivity. It magnetises strongly when current flows and demagnetises when current stops. Steel has high retentivity, so it retains magnetism — desired for permanent magnets, not for switchable electromagnets.
Q2. State Curie’s law for paramagnets.
χ = C/T, where C is the Curie constant and T is absolute temperature. Magnetisation in paramagnets falls inversely with temperature.
Q3. What is the difference between magnetic intensity (H) and magnetic field (B)?
B = μ₀(H + M) where H comes from free currents alone and M is the magnetisation contribution from material’s response. H is “applied” field (A/m); B is total flux density (Tesla).
Q4. What is the magnetic dip at the equator?
Zero. At the magnetic equator, the field is purely horizontal, so the angle of dip δ = 0°.
Q5. What does the area inside a hysteresis loop represent?
Energy dissipated as heat per unit volume per cycle of magnetisation-demagnetisation. Larger area = more energy loss — undesirable in transformer cores.
Practice MCQs
[cg_quiz id=”jee-magnetism-matter-2027″]
Related Reading
- JEE Rotational Motion 2027
- JEE Thermodynamics 2027
- JEE Electrochemistry 2027
- JEE Main 2027 Syllabus
- Free JEE Mock Test
Bottom line: Lock the dia/para/ferro classification table, hysteresis terms (Br, Hc), and Earth-magnetism formulae — that’s 100% of the JEE Main 2027 questions from this chapter.