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Basic Properties of Magnets
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Basic Properties of Magnets
Source of Magnetism in Iron Objects
Jun 18, 2008 © Harry P. Schlanger
Magnets are fascinating objects for anyone ranging from the child to the engineer. They can be
a source of fun and one can also probe and quantify their curious properties.
Everyone has observed magnets attracting iron objects and knows that magnetic fields are invisible force
fields. When iron filings are used, magnets disturb the filings to reveal lines of force (Fig 1). What
is less familiar is the source of the magnetism.
Common Properties of Magnets
A feature of magnets is the ends acting differently from each other. While one end attracts, the
other end repels. Thus magnet ends are called "poles", and in particular, a magnet itself is referred
to as a "dipole".
Figure.1 Lines of Force surrounding
a Magnet
An interesting aspect of magnets is when suspended by a string, they always align themselves in a
North-South direction. For this reason, magnet poles are correspondingly labelled North and South.
Lines of force emanate from the North pole and return to the South pole.
Figure 2. Unagnetized Domains
- random directions
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Figure 3. Magnetized Domains
- net magnetic field
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Source of Magnetism
If one was inquisitive, it would be tempting to see what happens if a magnet is chopped in pieces.
Surprisingly, each piece retains its magnetic properties, no matter how small the piece. This gives
the idea that at the microscopic level, there must be some fundamental magnetic domain
(as shown in Fig 2 & 3 above).
According to what is known about magnetic objects:
- When an iron object is unmagnetized, the domains consisting of N-S dipoles, lie in random directions
- When the object is placed in a magnetic field, the internal domains line up with each other, giving
rise to a net magnetic field
This magnetic field is said to be induced by the external field of the magnet. As soon as the external
magnet is removed, the object is observed to lose its magnetism: domains return to their random states
and the induced field disappears. The object only makes a temporary magnet.
So how are permanent magnets created? Permanent magnets, or lodestones, exist naturally or permanent
magnets are produced from the tempering process of ferrous metals, such as iron, iron alloys, nickel and
cobalt..
External Magnetic Fields
For a suspended magnet located in the Southern Hemisphere of the earth, the North pole of the magnet is
observed to point North and up slightly; conversely, if the magnet is located in the Northern Hemisphere,
the North pole of the magnet will still point North but down. This phenomenon is due to the lines of force
in the external magnetic field; that of the earth.
To determine the direction of any external magnetic field, whether from the earth or some other magnetic
field, a "test" magnet can be used (c.f. a compass). When the test magnet is placed at some angle to the
field, a torque on the magnet is observed which aligns it in the direction of the external field. By
convention, the direction of the external field is that which the North pole of the test magnet is
pointing to.
Magnets in Science and Daily Life
The study of magnets and magnetic fields is of great interest not only to scientists interested in the
physics, engineers interested in industrial magnets, but also to everybody ranging from the ordinary
person to the electronics enthusiast.
The reader may be interested in the discovery of the
electromagnetic field surrounding a wire, and how a current in the electromagnetic field produces a
magnetic force. This lead to the invention of the electric motor.
The copyright of the article Basic Properties of Magnets is owned by Harry P. Schlanger.
Permission to republish in print or online must be granted by the author in writing.
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