Magnetism and Matter – Notes

Magnetic properties of materials
When a diamagnetic material comes in contact with a magnet, it develops repulsion.
When a paramagnetic material comes in contact with a magnet, it develops a weak magnetic attraction.
When a ferromagnetic material comes in contact with a magnet, it develops a strong magnetic attraction.
The temperature beyond which a ferromagnetic material becomes a paramagnetic material is called Curie’s Temperature.
For a given value of magnetic intensity (H) the magnetic field (B) depends on the previous history of the sample. This phenomenon is called hysteresis.
Ferromagnets stay magnetized after being subjected to an external magnetic field, and this tendency to retain magnetism even after the external magnetic field is removed is called retentivity.
According to Curie’s law, the magnetic susceptibility, χ = C(µ0)/T

The dipole in a magnetic field
Two equal and opposite forces acting on a compass needle constitutes a couple.
τ = F x d
τ = M x B