Magnetism Types of Magnets Permanent Magnets magnetic once

Magnetism

Types of Magnets �Permanent Magnets (magnetic once magnetized) Ferromagnetism � Neodymium Iron Boron (Nd. Fe. B or NIB) � Samarium Cobalt (Sm. Co) � Alnico � Ceramic or Ferrite (Iron, Cobalt, Nickel) �Temporary Magnets – induced from magnetic field Diamagnetism – found in all matter (very small) Paramagnetism – stronger than diamagnetism (unpaired e-) �Electromagnets

Properties of Magnets �Magnets have two opposite poles. north south �Magnets exert forces on each other. Like poles repel Unlike poles attract. �The forces depend on the alignment of the poles.

The force between two magnets �The strength of the force between magnets depends on the distance between them. �The magnetic force decreases with distance much faster than does either gravity or the electric force.

Magnetic Fields �All magnets create a magnetic field in the space around them, and the magnetic field creates forces on other magnets. �The closer the lines are together, the stronger the field. �Magnetic field lines always point away from a magnet’s north pole and toward its south pole.

Earth’s Magnetic Field �Moving molten iron and in nickel Earth’s outer core causes most of Earth’s magnetic field. �Field has direction: lines point away from N and toward S. �Poles have switched in the past.

Cause of Magnetism �Magnetic fields are produced by moving electric charges. � There are two ways in which electrons create magnetism: 1. 2. Electrons around the nucleus and their motion makes the entire atom a small magnet. Electrons themselves act as though they were magnets. �In most materials, electron spin contributes more to magnetism than electron orbital motion. �Electrons are (very) tiny magnets.

Cause of Magnetism �Electrons with opposite spins (paired e-) cancel each other’s magnetic fields. �Electrons with spins aligned (unpaired e-) strengthen each other’s magnetic fields. �unpaired electrons can give the atoms an overall magnetic field.

Magnetic Domains �Atoms with similar magnetic orientations line up with neighboring atoms in groups called magnetic domains. �All of the domains of a magnetic substance tend to align themselves in the same direction when placed in a magnetic field.

Electricity and Magnetism �When an electric current passes through a wire a magnetic field is formed. Right hand rule – wrap in direction of magnetic field, thumbs points to magnetic north

Electromagnet �When an electric current is passed through a coil of wire wrapped around a metal core, a very strong magnetic field is produced. This is called an electromagnet.

Electromagnets �Changing the strength of an electromagnet Change the voltage Change the number of loops