Magnetism

Key Terms

Magnet: A material or object that generates a magnetic field. This field is invisible but is responsible for the notable force that pulls on ferromagnetic materials and repels or attracts other magnets.
Magnetic Field: A region around a magnetic material or a moving electric charge within which the force of magnetism acts.
Magnetic Poles: Refers to the two ends of a magnet, termed as North (N) and South (S) poles. The rule is that like poles repel and unlike poles attract.

Law of Magnets: Magnets always have two poles - a north and a south pole. If a magnet is cut into pieces, each piece still has both north and south poles.
Law of Magnetic Force: This describes the behaviour of magnets. Like poles repel each other, unlike poles attract each other.

Magnetic Domains: In ferromagnetic substances, magnetic fields of individual atoms are aligned in small areas known as magnetic domains. When the substance is magnetised, these domains align in the same direction.
Permanent Magnets & Temporary Magnets: Permanent magnets retain their magnetism once they are magnetised. Temporary magnets become magnets when they are in a magnetic field and lose their magnetism when the magnetic field disappears.
Earth’s Magnetic Field: The Earth acts as a giant magnet with its magnetic poles near the geographic North and South poles. Compasses align with this magnetic field.

Magnetic Fields and Field Lines: The region around a magnet where it can exert force is its magnetic field. The direction and strength of this field is represented by magnetic field lines. Remember that these lines go out from the North pole and come in to the South pole.
Magnetisation: Certain materials can be magnetised when placed in a magnetic field. This happens due to the alignment of the magnetic domains present in these materials.
Demagnetisation: A magnet can lose its magnetisation if it’s heated, hammered or dropped. The action can misalign the domains.

The strength of a magnetic field can be measured using a magnetometer. The units of this magnetic field strength are Tesla (T).

Gauss to Tesla: 1 Tesla = 10,000 Gauss. Gauss is the unit used in the CGS system of units (Centimeter Gram Second), while Tesla is used in SI. Use the correct units and be prepared to convert when appropriate.