Comparing Diamagnetic, Paramagnetic, and Ferromagnetic Response
Diamagnets have chi_m < 0 and mu_r < 1; paramagnets have small chi_m > 0 and mu_r slightly above 1; ferromagnets have large, nonlinear, history-dependent response below Curie temperature.
Why this shows up in the exam
Identifying materials from field-line diagrams · Matching properties to material classes · Predicting attraction or repulsion in non-uniform fields
Learn the idea
The sign and size of susceptibility determine how materials redirect field lines and respond to gradients. Diamagnets weakly expel field, paramagnets weakly concentrate it, and ferromagnets concentrate it very strongly and nonlinearly. Field-line sketches show these differences visually.
🧠 Memory hook: Dia diverts, para gathers a little, ferro gathers strongly.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- mu_r = 1 + chi_m — linear-material comparison of response
- chi_dia < 0 < chi_para << chi_ferro — qualitative susceptibility ordering outside saturation
- chi_m = M/H — susceptibility sign and size compare material response in the linear regime
How to approach it
- 1Read the sign and approximate size of susceptibility
- 2Inspect whether field lines avoid or concentrate in the sample
- 3Use temperature and hysteresis clues to separate para from ferro
Common slip-ups that cost marks
- •Treating paramagnets as strongly attracted like ferromagnets
- •Assuming ferromagnetic response is always linear
- •Reversing field-line concentration for dia- and paramagnets
🌟 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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