Physics · Magnetism And Matter · NEET
It depends on the x-axis. χ = C/T. If you plot χ against T (absolute temperature), you get a rectangular hyperbola — a curve that falls as T rises and never touches the axes. If you plot χ against 1/T, you get a straight line passing through the origin with slope equal to the Curie constant C. NEET usually shows the χ-vs-1/T straight line, so read the x-axis label first.
A paramagnet has tiny atomic magnets (dipoles) that try to line up with the applied field. Higher temperature means more random thermal motion, which shakes the dipoles out of alignment. So the net magnetisation M for the same field H drops, and since χ = M/H, susceptibility falls. That is why χ is inversely proportional to T.
No. Curie's law (χ = C/T) applies only to paramagnetic materials. Diamagnetism comes from induced currents in electron orbits, not from aligning dipoles, so a diamagnet's small negative χ is almost independent of temperature. Do not use χ = C/T for diamagnetic materials in NEET.
Curie's law is χ = C/T for paramagnets. Curie temperature (T_c) is a special temperature for ferromagnets: above T_c a ferromagnet loses its strong magnetism and behaves like a paramagnet, following the Curie-Weiss law χ = C/(T − T_c). So Curie's law is about paramagnets; Curie temperature is a threshold for ferromagnets.
The variation of magnetic susceptibility (χ) with absolute temperature (T) for a paramagnetic material is best represented by a graph in which:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
C is a positive material-dependent constant in Curie's law χ = C/T. It is the slope of the χ-vs-(1/T) straight-line graph. Larger C means a stronger paramagnetic response at a given temperature.
Magnetic susceptibility χ is dimensionless (no units) because it is the ratio M/H, and both magnetisation M and magnetic intensity H have the same unit, ampere per metre (A/m).
For a paramagnet χ is small and positive, so C/T is positive and the graph stays in the positive-χ region. Diamagnets have small negative χ and do not follow Curie's law.
For a ferromagnet above its Curie temperature T_c, susceptibility follows χ = C/(T − T_c). This is the Curie-Weiss law; it reduces to ordinary Curie's law when T_c is zero.
