Diamagnetism is the weak property of some materials (like bismuth, copper, water) to be REPELLED by a magnet. Their atoms have zero net magnetic moment; an applied field induces a tiny moment OPPOSITE to the field (Lenz's law), so susceptibility χ is small and negative (about −10⁻⁵). Memory hook: "DIA = DENY the field" — diamagnets push the field away and move from strong to weak field.
A diamagnetic bar pushes the external field lines out (field inside is reduced). The induced moment opposes B, so the bar is repelled and drifts from the strong-field region toward the weak-field region; χ is small and negative.
Your doubts, answered
Is a diamagnetic material attracted or repelled by a magnet?
It is weakly REPELLED. Unlike iron (which a magnet attracts), a diamagnetic bar is pushed away. In a non-uniform field it moves from the strong-field region to the weak-field region. This is the opposite of paramagnetic and ferromagnetic materials, which are attracted toward the stronger field.
Why is susceptibility (χ) negative for diamagnetic materials?
Susceptibility is χ = M/H. When you apply field H, the induced magnetisation M points OPPOSITE to H (because the field is set up to oppose the change, by Lenz's law). Since M and H are anti-parallel, M/H is negative. The value is tiny, about −10⁻⁵, so χ is small and negative (−1 ≤ χ < 0).
Do diamagnetic atoms have a permanent magnetic moment?
No. The defining feature is that each atom has ZERO net magnetic moment when no field is applied (the electron orbital moments cancel). A moment only appears when an external field is switched on, and that induced moment opposes the field. This is why the effect is so weak.
What actually causes diamagnetism (the mechanism)?
Orbiting electrons act like tiny current loops. When a field is applied, electrons orbiting in one sense speed up and those in the opposite sense slow down (induced current, Lenz's law). The imbalance gives a net moment opposite to the applied field. Because it comes from induced currents, it is present in ALL substances, but is usually masked by stronger para/ferromagnetism.
Is diamagnetism present in every material?
Yes, diamagnetism is universal — it exists in every substance. But it is extremely weak (one part in 10⁵), so in paramagnetic or ferromagnetic materials it is completely overshadowed and cannot be observed. It only shows up clearly in materials that have no permanent atomic moment.
⚠️ The NEET trap ✗ Thinking diamagnetic materials have positive but small susceptibility, or that they are attracted like weak iron. ✓ Diamagnetic χ is NEGATIVE and small (−1 ≤ χ < 0); they are REPELLED and move from strong to weak field. Only paramagnetic (small +) and ferromagnetic (large +) have positive χ. A perfect diamagnet (superconductor) has χ = −1. 🧠 Sign of χ is the most tested trap in this chapter.
Real NEET questions
2016
The magnetic susceptibility is negative for:
A · diamagnetic material only ✓
B · paramagnetic material only
C · ferromagnetic material only
D · paramagnetic and ferromagnetic materials
Solution: Susceptibility χ = M/H. In a diamagnetic material the induced magnetisation M points opposite to the applied field H, so M/H is negative. Numerically χ ≈ −10⁻⁵ (range −1 ≤ χ < 0). Paramagnetic materials have small positive χ (about +10⁻⁵) and ferromagnetic materials have large positive χ. Therefore χ is negative for diamagnetic material only. Answer: A.
2018
A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current is switched on, the diamagnetic rod is pushed up, out of the horizontal magnetic field, gaining gravitational potential energy. The work required to do this comes from:
A · the lattice structure of the material of the rod
B · the magnetic field
C · the current source ✓
D · the induced electric field due to the changing magnetic field
Solution: Step 1: A diamagnetic material is repelled from the strong-field region toward weaker field, so the rod is pushed up and gains potential energy mgh. Step 2: A magnetic force does no net work on charges, so the energy cannot come from the field itself. Step 3: As the diamagnet moves, its induced currents change the flux; to keep the field steady the current source must supply extra energy. That energy raises the rod. Hence the work comes from the current source. Answer: C.
2024
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).
A · A-II, B-I, C-III, D-IV
B · A-III, B-II, C-I, D-IV
C · A-IV, B-III, C-II, D-I
D · A-II, B-III, C-IV, D-I ✓
Solution: Diamagnetic: small negative, so 0 > χ ≥ −1 → II. Ferromagnetic: very large positive, χ >> 1 → III. Paramagnetic: small positive, 0 < χ < ε → IV. Non-magnetic: χ = 0 → I. Matching gives A-II, B-III, C-IV, D-I. Answer: D.
Solved Magnetism And Matter NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What are common examples of diamagnetic materials?
Bismuth, copper, lead, silicon, water, sodium chloride, nitrogen (at STP), and gold. Bismuth is the strongest ordinary diamagnet. Superconductors are perfect diamagnets with χ = −1.
What is the value of susceptibility for a diamagnetic material?
It is small and negative, typically about χ = −10⁻⁵. The full range is −1 ≤ χ < 0, with χ = −1 only for a perfect diamagnet (superconductor).
Does temperature affect diamagnetism?
No, diamagnetism is almost independent of temperature. This is different from paramagnetism, whose susceptibility falls with temperature (Curie's law, χ = C/T). Temperature-independence is a quick way to identify diamagnetic behaviour.
What is a superconductor's link to diamagnetism?
A superconductor is a perfect diamagnet: it completely expels the magnetic field (χ = −1, μr = 0). This total expulsion is called the Meissner effect, and it lets a magnet float above a superconductor.
How is diamagnetic different from paramagnetic?
Diamagnetic atoms have zero permanent moment and are repelled (χ negative). Paramagnetic atoms have a permanent moment, are weakly attracted, and have small positive χ that decreases with temperature.
