You know that a bar magnet can repel or attract another magnet depending on the nature of poles of the other two magnets that are facing each other. When a bar magnet is suspended by thread, its one end always points towards the geographic North Pole, calledmagnetic North Poleand the other end always points towards the geographic South Pole, calledmagnetic South Poleof the magnet.

Like poles repel and unlike poles attract each other.

Take a drawing cardboard and sprinkle some iron filings on it. Notice the position of the iron filings as a whole. Now, take a bar magnet and slowly bring it below the cardboard. You will observe that the iron filings tend to attract towards the magnet.

It is observed that most of the iron filings align themselves at poles.What does the pattern represent?It represents that the magnet exerts a force around its body with a stronger force near the two poles. A magnet produces a magnetic field, which can be detected by the force exerted on the iron filings. The regular pattern of the iron filings on the board represents the lines of magnetic field or lines of magnetic force calledmagnetic lines.

How to determine the shapes of magnetic field lines of a bar magnet?

To understand the process, let us see this animation

Do you know the direction of a magnetic field inside the magnet?

Inside the magnet, magnetic field lines run from the South Pole to the North Pole where they emerge out. Therefore, we can say that magnetic field lines make closed curves.

The region where magnetic field lines are crowded has relatively greater strength. Hence, in a magnet, strength of the regions near the poles is greater than other regions.It should be noted that a compass needle cannot point in two directions when placed at a point near the magnet. This means that no two magnetic field lines cross each other at a point.

Characteristics of magnetic field lines

Magnetic field lines emanate from the North Pole and terminate at the South Pole of a magnet.The degree of closeness of magnetic field lines represents the relative strength of the magnet.No two field lines can intersect each other.

Magnetic field lines of the Earth

The Earth is treated as magnetic because it is assumed that a huge bar magnet is buried within its interior with the magnetic North Pole near the geographic South Pole, and the magnetic South Pole near the geographic North Pole respectively.

Since magnetic field lines originate from the magnetic North Pole and end at the magnetic South Pole, the Earths magnetic field lines originate from its geographic South Pole and end at its geographic North Pole respectively.

The magnetic poles of the Earth continuously change their position with time i.e., the magnetic North Pole becomes the magnetic South Pole and vice-versa. This phenomenon of flipping of poles is known asmagnetic reversal. It is assumed by scientists that the Earths magnetic field has undergone 170 such reversals in the past 100 millions years.

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