Magnetic field :
The space surrounding a magnet in which magnetic force is exerted , is called a magnetic field. Magnetic field has both , magnitude as well as direction.
James Clerk Maxwell frst described the underlying unity of electricity and magnetsm in the 19th century.
Like poles repel each other and unlike poles atract each other and Magnetc poles cannot be isolated.
Compass :
A compass is a device used to show magnetic field direction at a point. A compass is also known as a plotting compass.
A compass consists of a tiny pivoted magnet usually in the form of a pointer which can turn freely in the horizontal plane.
The tiny magnet of the compass is also called 'Magnetic needle'. The tip of compass needle points towards the north direction whereas its tail points in the south direction.
Magnetic field lines or Magnetic lines of force ) :
A magnetic line of force is the line tangent to which at any point gives the direction of the magnetic field at that point.
The compass needle always sets itself along the line tangential to it.
1.To plot the magnetic field pattern Due to a bar Magnet by using Iron filing :
Iron filings show the shape of magnetic field produced by a bar Magnet by aligning themselves with the magnetic field lines.
2. To plot the magnetic field pattern Due to a Bar magnet by using a compass :
The magnetic field pattern around a bar Magnet is shown in figure. This has been traced by using a plotting compass. By doing this we get the various dots A, B, C, D, E, F, G, H, I, J, K and L, all denoting the path in representing a magnetic field line , which begins on the North pole of the bar Magnet and ends on its south pole.
Properties ( or characteristics ) of the magnetic field Lines :
1. They run from the North pole to the south pole outside the magnet and from south pole to North pole inside the magnet.
2. The magnetic field lines come closer to one another near the poles of a magnet but they are widely separated at other places.
3. Magnetic line of force are imaginary lines
4. Two magnetic lines of force do not intersect each other
5. They tend to contract longitudinal.
6. They tend to exert lateral pressure on the neighbouring fields lines.
7. The strength of magnetic field is indicated by the degree of closeness of the field lines. Where the field lines are closest together , the magnetic field is the strongest.
Magnetic field of Earth :
The Earth itself behaves as a magnet which causes a freely suspended magnet to point always in a North - South direction Even in the absence of any other magnet.
The shape of the Earth's magnetic field resemble that of an imaginary bar Magnet of length one-fifth of earth's diameter buried at its centre.
The Axis of earth's magnetic field is inclined at an angle of about 15° with the geographical axis.
Earth's magnetism is due to the magnetic effect of current ( which is flowing in the liquid core at the centre of the earth). This earth is a huge electromagnet.
