What is a Magnetic Field?
Stephen Hawking explains in his book, A Brief History Of Time that virtual photons are the force carrying particles of the electromagnetic field. The 4 forces in nature can be explained by exchanges of particles, but quantum gravity theory has problems and is not complete. Richard Feynman refers to photons from a magnet in his book, Q.E.D., The Strange Theory of Light and Matter. Feynman explains that under certain circumstances, including when a very large number of electrons are all moving in the same way, such as going around in the coils of an electromagnet, a large number of photons are emitted, all of exactly the same kind. Roger Penrose explains in his book, The Emperor’s New Mind that the momentum state wave function of a photon is a corkscrew or helix. He also explains that all emitted photons must carry some mass because E=mc2. Think of energy as a highly diluted form of mass or think of mass as a highly concentrated form of energy. Thus one can visualize magnetic attraction
Magnetic fieldsA field of force that is generated by electric currents. The Sun’s average large-scale magnetic field, like that of the Earth, exhibits a north and a south pole linked by lines of magnetic force. are created by things that are magnetic (like iron magnets) or by moving charged particles. A magnetic field is the description of the force a magnetic object exerts in the space surrounding the magnetic object. A force is a push or pull. To learn more about forces and magnetic fields, please visit www.colorado.edu/physics/2000/waves_particles/. When charged particles move around really fast they create magnetic fields.
Magnetism has been known for thousands of years, though until relatively recently (ca. 1820) the only magnets were naturally occurring magnetic rocks called “lodestones” (magnetite). The word “magnetism” derives from the district of Magnesia in Asia Minor where lodestones were found. These lodestones were observed to attract bits of iron, just like a kitchen magnet which is attracted to your refrigerator door. The space around the magnet is the site of the magnetic field, where the magnetic force is felt by the bit of iron. At each point around the magnet, the magnetic field has both a strength and a direction.
We are surrounded by magnetic fields (both AC and DC) from the earth’s magnetic field to man-made sources such as magnets, motors and transformers. When a piece of sensitive equipment is being affected by these fields we need to produce a shield. Examples that are affected are cathode ray tubes, photomultiplier tubes, audio transformers, scanning electron microscopes, position sensors.
