Magnetism refers to physical phenomena arising from the force between magnets, objects that produce fields that attract or repel other objects.
All materials experience magnetism, some more strongly than others. Permanent magnets, made from materials such as iron, experience the strongest effects, known as ferromagnetism. This is the only form of magnetism strong enough to be felt by people.
Then there's paramagnetism, in which certain materials are attracted by a magnetic field, and diamagnetism, in which materials are repelled by a magnetic field. Other, more complex, forms include antiferromagnetism, in which the magnetic properties of atoms or molecules align next to each other; and spin glass behavior, which involve both ferromagnetic and antiferromagnetic interactions.
Some materials are called non-magnetic, because their magnetic effects are so small. Magnetism can also vary depending on temperature and other factors.
A magnetic field is a way of mathematically describing how magnetic materials and electric currents interact. Magnetic fields have both a direction and a magnitude, or strength. Magnets have a "north" pole and a "south" pole. Opposite poles attract each other and alike poles repel each other. These poles are referred to as a magnetic dipole. Magnetic dipoles and electric currents both give rise to magnetic fields.
A magnet is what makes a compass point north — the small magnetic pin in a compass is suspended so that it can spin freely inside its casing and respond to our planet's magnetism. A compass needle aligns itself and points toward the top of Earth's magnetic field.
Magnetic fields exert a force on particles in the field, called the Lorentz force. The motion of electrically charged particles gives rise to magnetism. The magnetic force acting on a single electric charge depends on the size of the charge, its speed, and the strengths of the electric and magnetic fields.
Electricity and magnetism
Both electric and magnetic interactions are elements of a single phenomenon called electromagnetism. There are four fundamental forces: the strong force, the weak force, gravitation and the electromagnetic force. The field of electromagnetism deals with how electrically charged particles interact with each other and with magnetic fields.
James Clerk Maxwell developed a unified theory of electromagnetism in 1873. There are four main electromagnetic interactions:
- The force of attraction or repulsion between electric charges is inversely proportional to the square of the distance between them.
- Magnetic poles comes in pairs that attract and repel each other much as electric charges do.
- An electric current in a wire produces a magnetic field whose direction depends on the direction of the current.
- A moving electric field produces a magnetic field, and vice versa.
Maxwell developed a set of formulas, called Maxwell's equations, to describe these phenomena.