Diamagnetism
Diamagnets have small negative susceptibility, relative permeability slightly below one, and magnetization opposite to H. Ideal perfect diamagnetism has chi_m = -1 and B = 0 inside under the idealized bulk conditions.
Why this shows up in the exam
Classifying magnetic materials · Magnetic levitation demonstrations · Interpreting field-line exclusion from samples
Learn the idea
A diamagnetic material develops a weak induced magnetization opposite to the applied field. An applied field slightly changes electron motion so that the induced magnetic response opposes the change. The sample is therefore weakly pushed toward lower-field regions.
🧠 Memory hook: Dia disagrees with the applied field.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- M = chi_m H with chi_m < 0 — opposing diamagnetic magnetization
- mu_r = 1 + chi_m < 1 — relative permeability of an ordinary diamagnet
- F toward weaker field — qualitative motion in a non-uniform field
How to approach it
- 1Look for induced opposition to H
- 2Use chi below zero and mu_r below one
- 3In a gradient, choose motion toward weaker field
Common slip-ups that cost marks
- •Calling diamagnets strongly attracted
- •Assigning positive susceptibility
- •Claiming ordinary diamagnetism strongly depends on 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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