Magnetism

Magnetic fields are created only by moving charges (unlike electric fields, from static or moving charges). Unit: tesla (T).
Materials: diamagnetic (weakly repelled, no residual magnetism), paramagnetic (weakly attracted, no residual magnetism), ferromagnetic (strongly attracted, retains magnetism).
Straight wire field: B = μ0I/(2πr). Circular loop center field: B = μ0I/(2r).
Magnetic force on a moving charge: FB = qvB sin θ — max at 90°, zero at 0°. Same angle dependence for a current-carrying wire: FB = ILB sin θ.
Right-hand rule differs by case: moving charge (fingers = v, curl toward B, thumb = F) vs. current-carrying wire (thumb = I, curl fingers toward B, palm = F).

B = μ0I/(2πr) | B = μ0I/(2r) | FB = qvB sin θ | FB = ILB sin θ

Material	Behavior
Diamagnetic	All electrons paired; weakly repelled; no residual magnetism
Paramagnetic	Unpaired, randomly oriented electrons; weakly attracted; no residual magnetism
Ferromagnetic	Unpaired, self-aligning electrons; strongly attracted; retains magnetism (iron, cobalt, nickel)

Don't mix up the two right-hand rules — moving-charge case starts with fingers along v; current-wire case starts with thumb along I. Using the wrong one flips the answer.
Magnetic fields act only on moving charges — a stationary charge in a magnetic field feels zero magnetic force, even in a strong field.
At θ = 0° (velocity or current parallel to B), magnetic force is zero, not maximum — easy to reverse-confuse with the θ = 90° maximum.

A charge moves parallel to a magnetic field. What magnetic force does it feel?

What distinguishes ferromagnetic materials from paramagnetic ones?

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