Engineering Physics I - Magnets and Magnetism

 

Magnets and Magnetic Fields

Magnetic pole 

The property of magnet to attract small pieces of iron seems to be concentrated in small regions of  the magnet. These regions are called magnetic poles.

A magnet has two poles : i) North pole    and    ii) South pole

Magnetic lines of force emerge out from N-pole and converge into S-pole.

fig.: Bar magnet 

Magnetic Dipole

A system of two equal and opposite magnetic poles separated by certain distance is called magnetic dipole.

Consider a magnetic dipole consisting of two magnetic poles, north and south each of strength ‘m’ and separated by distance ‘2l’.

Magnetic Dipole Moment

It is defined as the product of strength of either pole and the distance between the magnetic poles.

It is denoted by ‘M’ and given as,

       M = m x 2l

fig. : Magnetic dipole 

The strength of pole ‘m’ is measured in Weber(Wb) or Ampere meter (Am) in SI. Therefore, the unit of ‘M’ is Weber meter (Wbm) or Ampere meter² (Am²) in SI.

Axial Line

The imaginary line joining two poles of magnet is known as axial line of magnet.

Equatorial line

The line perpendicular to the axial line and passing through the midpoint of the axial line is called equatorial line.

Equivalent length 

The distance between the two poles of a magnet is called equivalent length or effective length of the magnet.

It is equal to 2l as shown in the figure.

Geometrical length

The real length of  a magnet between the two ends is called geometrical length of the magnet.

Experimentally, it has been found that,

  2l = 0.85 x L

where, L = geometrical length of magnet

           2l = effective or equivalent length or real length of magnet