Physics · Magnetism And Matter · NEET
| Susceptibility χ (= M/H) | Dia: small negative (−1 ≤ χ < 0) · Para: small positive | Ferro: very large positive (χ >> 1) |
| Behaviour near a magnet | Dia: weakly repelled · Para: weakly attracted | Ferro: strongly attracted |
| Relative permeability μ_r = 1 + χ | Dia: slightly < 1 · Para: slightly > 1 | Ferro: >> 1 |
| Effect of temperature | Dia: almost none · Para: χ = C/T (Curie's law) | Ferro: ferromagnetic only below Curie temp T_c |
| Examples | Dia: bismuth, copper, water · Para: aluminium, oxygen | Ferro: iron, cobalt, nickel |
Repelled. A diamagnetic material develops a weak magnetisation that OPPOSES the applied field, so it is pushed slightly away from the magnet. In a non-uniform field it moves from the strong-field region toward the weak-field region. Paramagnetic and ferromagnetic materials do the opposite: they are attracted toward the strong field.
χ = M/H. In a diamagnetic material the induced magnetisation M points OPPOSITE to H, so M/H is negative (0 > χ ≥ −1). In a paramagnetic material the atomic dipoles align WITH H, so M is along H and χ is a small positive number. Ferromagnetics align very strongly, giving χ >> 1.
Both are attracted to magnets and have positive χ, but the size is very different. Paramagnetic χ is tiny (like 10⁻³ to 10⁻⁵) and the material loses magnetism the moment the field is removed. Ferromagnetic χ is huge (hundreds to thousands) because of aligned domains, and the material can stay magnetised (permanent magnets). Iron, cobalt, nickel are ferromagnetic.
Only ferromagnetic materials have χ >> 1 (much greater than one). Diamagnetic χ is a small negative number and paramagnetic χ is a small positive number close to zero. This single fact answers most NEET match-the-column questions.
No, diamagnetism is nearly independent of temperature because it comes from induced electron currents, not from thermal alignment of dipoles. Paramagnetic χ follows Curie's law χ = C/T (falls as T rises). Ferromagnetics stay ferromagnetic only below the Curie temperature; above it they become paramagnetic.
The magnetic susceptibility is negative for:
Match List-I (Material) with List-II (Susceptibility χ): A. Diamagnetic B. Ferromagnetic C. Paramagnetic D. Non-magnetic ; I. χ = 0 II. 0 > χ ≥ −1 III. χ >> 1 IV. 0 < χ < ε (small positive):
An iron rod of susceptibility 599 is subjected to a magnetising field of 1200 A m⁻¹. The permeability of the material of the rod is (μ₀ = 4π × 10⁻⁷ T m A⁻¹):
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Diamagnetic: bismuth, copper, water, gold. Paramagnetic: aluminium, sodium, oxygen, platinum. Ferromagnetic: iron, cobalt, nickel, gadolinium. Iron rusting aside, remember Fe-Co-Ni as the classic ferromagnetic trio for NEET.
Diamagnetic: −1 ≤ χ < 0 (small negative). Paramagnetic: 0 < χ < ε, a small positive number (order 10⁻³ to 10⁻⁵). Ferromagnetic: χ >> 1 (hundreds to thousands). Relative permeability μ_r = 1 + χ: dia μ_r slightly less than 1, para slightly more than 1, ferro much greater than 1.
Diamagnetic materials move from the strong-field region to the weak-field region (repelled). Paramagnetic and ferromagnetic materials move from the weak-field region to the strong-field region (attracted), with ferromagnetics feeling a much larger force.
A superconductor is a PERFECT diamagnet. It has χ = −1 and μ_r = 0, so it expels the magnetic field completely from its interior (Meissner effect). It is the extreme case of diamagnetism.
Diamagnetism is almost temperature-independent. Paramagnetic χ = C/T decreases as temperature rises (Curie's law). Ferromagnetic materials remain ferromagnetic only below the Curie temperature T_c; above T_c they turn paramagnetic.
