Moving Charge and Magnetism
Magnetism is a phenomenon produced by the motion of electric charge, which results in attractive and repulsive forces between objects.
A magnet is any piece of material that has the property of attracting iron (or steel). Magnetite, also known as lodestone, is a naturally occurring rock that is a magnet. This natural magnet was first discovered in a region known as magnesia and was named after the area in which it was discovered. Magnetism may be naturally present in a material or the material may be artificially magnetized by various methods.
Magnets may be permanent or temporary. After being magnetized, a permanent magnet will retain the properties of magnetism indefinitely. A temporary magnet is a magnet made of soft iron, that is usually easy to magnetize; however, temporary magnets lose most of their magnetic properties when the magnetizing cause is discontinued. Permanent magnets are usually more difficult to magnetize, but they remain magnetized. Materials which can be magnetized are called ferromagnetic materials.
The force exerted on a charged particle by a magnetic field is given by the vector cross product: F = q ( v x B ) F = force (vector) q = charge on the particle (scalar) v = velocity of the particle relative to field (vector) B = magnetic field (vector)
The Biot-Savart law asserts that the magnetic field dB due to an element dl carrying a steady current i at a point P at a distance r from the current element is:
