Homing pigeon enthusiast knows that if pigeons released hundreds of kilometers away, they will automatically homing. Pigeons: why has such a good ability to identify the home? It turns out that pigeons are sensitive to the Earth's magnetic field, they can take advantage of changes in the Earth's magnetic field to find his home. If you Dove head tied to a magnet, pigeon will trek. If the pigeons fly over the radio tower, strong electromagnetic interference will make them lose their way.
In medicine, abnormal tissue using MRI to diagnose the human body to determine diseases, this is the more familiar magnetic resonance imaging technology, its basic principle is as follows: with a positive charge of the nucleus, and spin motion. Normally, nuclei spin axis alignment is erratic, but when you place it in an external magnetic field, and spatial orientation of nuclear spin transitions from disorder to order. Magnetization vector spin systems growing from zero, when the system reaches equilibrium magnetization intensity reaches a stable value. If the nuclear spin systems by external effects, such as certain frequencies of radio frequency excited nucleus can cause resonance effects.