Electromagnetic field

An Electromagnetic field is the force between particles possessing charge. There are two types of charges, designated positive and negative. Particles with the same charge repel each other while particles of opposite charge attract. The magnets people are familiar with are due to polarizing the mass of the object, most often iron.

The equation for calculating the force from a given charge is Coulomb's law:

where q1 and q2 are the respective charges of the two particles, r is the distance between them and ε0 is the electric constant: 8.854E-12 C²/(N*m²)

Magnets in use

Most people are familiar with simple horseshoe and bar magnets, and the magnets they stick on their refrigerator. A compass is made from a small free-spinning magnet that aligns itself with the Earth's own magnetic field.

Electromagnets are created by sending an electric current through a coil of wire that produces a magnetic field. They are often used in construction.

Moving a magnet through a coil of conducting wire can achieve the reverse effect. To generate electricity, a magnet is spun in the coil and a current is generated. Metal detectors operate on a similar principle. As a piece of metal passes through the detector, it generates a current and the alarm goes off.