# Bloch equations

### From NMR Wiki

Bloch equation describes evolution of classical magnetic moment in the magnetic field. The equation in the absence of T1 and T2 relaxation is:

## Summary explanation

A particle with a magnetic moment **M** in the magnetic field **B** will
experience change of its mechanical angular moment **J**, i.e. torque = dJ/dt.

Wigner-Eckart theorem in quantum mechanics proves that particle's magnetic moment is collinear with it's angular moment so that:

,

where γ is the scalar quantity called gyromagnetic ratio of the particle.

Therefore we have expression (known as **Bloch Equation**):