NCERT Book Class 12 Physics Chapter 5 Magnetism and Matter

Physics

Chapter Five

MAGNETISM AND
MATTER

5.1 INTRODUCTION
Magnetic phenomena are universal in nature. Vast, distant galaxies, the
tiny invisible atoms, humans and beasts all are permeated through and
through with a host of magnetic fields from a variety of sources. The earth’s
magnetism predates human evolution. The word magnet is derived from
the name of an island in Greece called magnesia where magnetic ore
deposits were found, as early as 600 BC.
In the previous chapter we have learned that moving charges or electric
currents produce magnetic fields. This discovery, which was made in the
early part of the nineteenth century is credited to Oersted, Ampere, Biot
and Savart, among others.
In the present chapter, we take a look at magnetism as a subject in its
own right.
Some of the commonly known ideas regarding magnetism are:
(i) The earth behaves as a magnet with the magnetic field pointing
approximately from the geographic south to the north.
(ii) When a bar magnet is freely suspended, it points in the north-south
direction. The tip which points to the geographic north is called the
north pole and the tip which points to the geographic south is called
136 the south pole of the magnet.