Susceptibility Sign and Value for Each Material Type
Physics · Magnetism And Matter · NEET
Magnetic susceptibility chi = M/H tells you how a material responds to a field. Diamagnetic: small and NEGATIVE (about -10^-5, and exactly -1 for a superconductor). Paramagnetic: small and POSITIVE (about +10^-5). Ferromagnetic: large and POSITIVE (thousands). Memory hook: "Dia is the only Down (negative); Para is small Plus; Ferro is a Fat Plus."
Number line of magnetic susceptibility (chi): diamagnetic sits on the negative side (down to -1 for a superconductor), while paramagnetic is a small positive value and ferromagnetic is a large positive value.
Your doubts, answered
Which material has NEGATIVE susceptibility?
Only diamagnetic materials have negative chi. Because chi = M/H, a negative value means the magnetisation M points opposite to the applied field H. Diamagnets are the only class where M opposes H, so they are the only ones with negative susceptibility. Paramagnetic and ferromagnetic materials both have positive chi (M is along H).
What are the actual numbers for each type?
NCERT gives clear values. Diamagnetic: chi is about -10^-5 (small negative). Paramagnetic: chi is about +10^-5 (small positive). Ferromagnetic: chi is large and positive, often 1000 or more. A superconductor is a perfect diamagnet with chi = -1 exactly (field fully expelled).
Why is paramagnetic and diamagnetic susceptibility almost the same size but opposite sign?
NCERT states a tiny difference in chi gives very different behaviour: diamagnetic chi = -10^-5 versus paramagnetic chi = +10^-5. The magnitudes are similar because both effects are weak; the SIGN is what separates them. Negative means repelled (moves to weaker field), positive means weakly attracted (moves to stronger field).
Can susceptibility be less than -1?
No. For diamagnets chi lies in the range -1 <= chi < 0. The most negative possible value is -1, reached only by a superconductor (perfect diamagnet), where mu_r = 0 and the field is totally expelled. Ordinary diamagnets are far from -1, only about -10^-5.
Is susceptibility a vector or does it have units?
chi is a pure number (dimensionless) because chi = M/H and both M and H have the same unit (A/m). So chi has no unit and no direction; only its sign and size matter. This is a common one-mark trap.
⚠️ The NEET trap ✗ Thinking paramagnetic materials can have negative susceptibility because they are 'weakly' magnetic. ✓ Paramagnetic chi is small but always POSITIVE (M is along H). Only diamagnetic materials have negative chi (M opposes H). 🧠 Weak does not mean negative. 'Weak' describes size; the SIGN is set by direction. Dia is the only Down.
Real NEET questions
NEET 2016 Phase 1
The magnetic susceptibility is negative for:
A · diamagnetic material only ✓
B · paramagnetic material only
C · ferromagnetic material only
D · paramagnetic and ferromagnetic materials
Solution: Step 1: Susceptibility chi = M/H, where M is magnetisation and H is magnetic intensity. Step 2: A negative chi means M points OPPOSITE to H. Step 3: Only in diamagnetic materials does the induced magnetisation oppose the applied field, so M and H are anti-parallel. Step 4: Paramagnetic and ferromagnetic materials have M along H, giving positive chi. Hence chi is negative for diamagnetic material only. Answer: A.
NEET 2024
Match List-I with List-II. List-I (Material): A. Diamagnetic, B. Ferromagnetic, C. Paramagnetic, D. Non-magnetic. List-II (Susceptibility chi): I. chi = 0, II. 0 > chi >= -1, III. chi >> 1, IV. 0 < chi < e (a small positive number). Choose the correct answer:
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: Step 1: Diamagnetic chi is small and negative, range 0 > chi >= -1, so A-II. Step 2: Ferromagnetic chi is very large and positive, chi >> 1, so B-III. Step 3: Paramagnetic chi is small and positive, 0 < chi < e, so C-IV. Step 4: Non-magnetic (like vacuum) has chi = 0, so D-I. Combining: 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.
Yes. chi = M/H and both M and H are measured in A/m, so chi is a pure number with no unit.
What is the susceptibility of a superconductor?
A superconductor is a perfect diamagnet with chi = -1, mu_r = 0 and mu = 0. It expels the external field completely (Meissner effect).
Which material has the highest susceptibility?
Ferromagnetic materials like iron, cobalt and nickel have the largest positive chi, often in the thousands.
Does temperature change susceptibility?
Yes for para and ferro. Paramagnetic chi falls as temperature rises (Curie's law, chi = C/T). Diamagnetic chi is almost independent of temperature.
What sign of chi means the material is attracted to a magnet?
Positive chi (para and ferro) means the material is attracted toward the stronger field. Negative chi (dia) means it is repelled toward the weaker field.
