If we hold the current carrying conductor in our right hand such that the thumb points in the direction of current flow, then the fingers encircling the wire points in the direction of the magnetic field lines produced.

The materials with high retentivity, high coercivity and high permeability are suitable for making permanent magnets.
Examples: Steel and Alnico.

The significance of hysteresis loop is that it provides information such as retentivity, coercivity, permeability, susceptibility and energy loss during one cycle of magnetisation for each ferromagnetic material. Therefore, the study of hysteresis loop will help us in selecting proper and suitable material for a given purpose.

It is defined as the ability of the materials to retain the magnetism in them even magnetising field vanishes.

(i) Uniform magnetic field: Magnetic field is said to be uniform if it has the same magnitude and direction at all the points in a given region.
Example, locally Earth's magnetic field is uniform.
(ii) Non-uniform magnetic field: Magnetic field is said to be non-uniform if the magnitude or direction or both varies at all its points.
Example: magnetic field of a bar magnet.

The magnetic flux density can also be defined as the number of magnetic field lines crossing unit area kept normal to the direction of line of force. 
Its unit is Wb m^-2 or telsa.

Magnetic field is the region or space around every magnet within which its influence will be felt by keeping another magnet in that region.
\(\vec { B } =\frac{1}{q_m}\vec{E}\)
Its unit is N A^-1m^-1

The component of Earth's magnetic field along the horizontal direction in the magnetic meridian is called horizontal component of Earth's magnetic field, denoted by B_H.

The angle subtended by the Earth's total magnetic field \(\vec { B } \) with the horizontal direction in the magnetic meridian is called dip or magnetic inclination (I) at that point.

The angle between magnetic meridian at a point and geographical meridian is called the declination or magnetic declination (D).

The straight line which connects magnetic poles of Earth is known as magnetic axis. A vertical plane passing through magnetic axis is called magnetic meridian and a great circle perpendicular to Earth's magnetic axis is called magnetic equator.

Day and night occur because Earth spins about an axis called geographic axis. A vertical plane passing through the geographic axis is called geographic meridian and a great circle perpendicular to Earth's geographic axis is called geographic equator.

There are three quantities required to specify the magnetic field of the earth on its surface, which are often called as the elements of the earth's magnetic field. they are
(a) Magnetic declination (D)
(b) Magnetic dip or inclination (I)
(c) the horizontal component of the Earth's magnetic field (B_H)

The branch of physics which deals with the Earth's magnetic field is called Geomagnetism or Terrestrial magnetism.

Gover suggested that the Earth's magnetic field is due to hot rays coming out from the Sun. These rays will heat up the air near equatorial region. Once air becomes hotter, it rises above and will move towards northern and southern hemispheres and get electrified. This may be responsible to magnetize the ferromagnetic materials near the Earth's surface.