1. Magnetism
Important Terms and Definitions
Two types of magnets: - natural and artificial
Natural magnets
The stones which possess the property to
attract other stones are called load-stones.
Where load stones are suspended freely, it
remained in equilibrium in north-south direction.
Magnetic dipole
An arrangement of two magnetic poles of equal
and opposite strengths separated by a finite
distance is called a magnetic dipole or a bar
magnet. The two magnetic poles of dipole are
called N-pole & S-pole
An isolated pole does not exist.

2. Poles are Fictitious :A bar magnet is assuming to have 2
opposite poles (N & S) situated near its
ends. If we try to separate the two poles by
cutting the magnet into two pieces, opposite
poles are found to appear at the broken
ends and each piece is again a new magnet
with opposite poles. Even if the magnet is
broken to the atomic level, it exists with two
poles. This shows that the two poles of a
magnet can not be separated from each
other. Thus, a single magnetic pole i.e.
monopole cannot exist. So, magnetic poles
always appear in pairs and hence any
magnet is called a dipole and it is said that,
a magnetic monopole doesn’t exist or poles
of a magnet cannot be separated.

3. Magnetic length
The distance between the two poles of a bar
magnet is called the magnetic length of the
magnet. It is a vector.
Direction S-pole to N-pole
Magnetic length = 5/6 (Geom. length)

4. Note
1. Pole strength (m)
The ability of a magnetic pole to produce
magnetic field around it is called magnetic
pole strength.
2. Axis of a magnetic dipole
A straight line passing through magnetic
poles of a magnetic dipole is called axis of a
magnetic dipole.
3. Equator of a magnetic dipole
A straight line passing through the centre of
a magnetic dipole and perpendicular to its
axis is called equator of a magnetic dipole.

5. Magnetic dipole moment (M)
The product of the strength of either pole and
the magnetic length of the magnet is called
magnetic dipole moment.
Magnitude
:
M = m × 2ℓ, where m = pole
strength of N-pole
Direction
:
S-pole of the magnet to its N-
:
Ampere meter2 (Am2)
pole
Unit

6. Magnetic field
The space around a magnet (or a conductor
carrying current) in which its magnetic effect
can be experienced, is called the magnetic
field.
The SI unit of strength of magnetic field (also
known as magnetic induction or magnetic flux
density) is tesla (T)
1 tesla (T) = 1 weba / metre2 = 1 wb/m2
1 tesla (T) = 1 N/Am........ {B = F/m, which is
the
B due to a role
strength}
10-4 tesla (T) = 1 gauss (G)

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