The compass needle shows almost the same direction along north and south at places far from the magnet.

• What does it mean?

From these observations we conclude that the strength of the field varies with distance from the bar magnet. Now hold the compass a little above the table and at the top of the bar magnet. You can observe that field exists in all directions around the bar magnet. Hence we can say that the magnetic field is three dimensional i.e., magnetic field surrounds its source such as bar magnet. From the above discussion we can generalize that:

A magnetic field exists in the region surrounding a bar magnet and is characterized by strength and direction.

1. How can we find the strength of the field and direction of the field? You know that the direction of the field can be determined by using a compass. Let us find out how to determine the strength of the field.

Place a white sheet of paper on a horizontal table. Place a compass in the middle of it. Put two dots on either side of the compass needle. Take it out. Draw a line connecting the dots which shows the North and South of the earth. Now place the bar magnet on the line drawn in such a way that its north pole points towards geographic north. Now place the compass at the north pole of the bar magnet. Put a dot at the north pole of the compass needle. Now remove the compass and place it at the dot. It will point in other direction. Again put a dot at the north pole of the compass needle. Repeat the process till you reach the south pole of the bar magnet. Connect the dots from "N"of the bar magnet to ‘S’ of the bar magnet. You will get a curved line. Now select another point from the north pole of the bar magnet. Repeat the process for many points taken near the north pole. You will get different curves as shown in figure2

• What are these curves?

Technically these curves are called “magnetic field lines”. Field lines are imaginary lines.So These lines help us to understand the nature of the field.