Paramagnetism and Curie's Law
A linear paramagnet has small positive susceptibility and M parallel to H. For an ideal Curie paramagnet, chi_m = C/T, so at fixed material density M is proportional to H/T.
Why this shows up in the exam
Temperature scaling of magnetization · Paramagnetic susceptibility calculations · Magnetic thermometry
Learn the idea
Paramagnets align weakly with a field, and their susceptibility usually decreases as temperature rises. Atoms with permanent moments tend to align with the field, but thermal agitation disrupts that order. A stronger field or lower temperature therefore gives greater magnetization in the Curie-law range.
🧠 Memory hook: Paramagnets follow the field, but heat scrambles them.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- chi_m = C/T — Curie's law for an ideal paramagnet
- M = chi_m H = C H/T — magnetization dependence on field and absolute temperature
- M2/M1 = (H2/T2)/(H1/T1) — comparison for the same Curie paramagnet
How to approach it
- 1Confirm the sample is paramagnetic
- 2Convert temperature to kelvin
- 3Use ratios of H/T before substituting constants
Common slip-ups that cost marks
- •Using Celsius instead of kelvin
- •Taking susceptibility as negative
- •Assuming Curie's law applies to ferromagnets below Curie temperature
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A charge of 2 microC moves perpendicular to a 3 T magnetic field at 4 x 10^5 m/s. Find the magnetic force.
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