# What Is Magnetic Field | Properties Of Magnet

## What Is Magnetic Field

Magnetic fields are caused by moving electric charges (current flows). In permanent magnets, electric currents are the cause of fields at the atomic level. Like the electric field, the magnetic field is also a force field. It can exert force on magnets, on magnetic materials, or on moving electric charges.

The unit of measurement of field strength is specified in amperes per meter (A/m). The term “magnetic flux density” is also frequently used in the Tesla (T) unit. Both the sizes can be easily converted into each other. In air or in biological tissue, 80 amperes per meter corresponds to about 100 microtesla, which is 0.0001 tesla.

If the flow of current is the cause of the magnetic field, then the strength of the magnetic field depends mainly on the strength of the current and the distance of the conductor.

Static and time-varying Magnetic Fields

A magnetic field is also called a stationary or a constant (direct) field if the field force remains constant over time.  A natural magnetic field, for example, is the Earth’s magnetic field. (Properties Of Magnet) It can be called a stable field because significant changes in field strength occur only over a very long period of time (a few thousand years).

When electric charges are transferred through lines, that is, when current flows, a magnetic field is created around the conductor. The greater the current strength, the greater the magnetic field strength.

If the current continuously changes its direction, as is the case with a technically generated 50 Hz alternating current, the magnetic field also changes in the same rhythm – we are dealing with an alternating magnetic field of the same frequency.

On the other hand, electric direct currents are surrounded by magnetic direct fields.

### Properties Of Magnet

1. Attraction

Magnet has the ability to attract pieces of metals like iron, steel etc. If a magnet is b)rought near a fine iron sawdust, the sawdust sticks to the magnet.

The amount of sticking dust is highest at both ends of the magnet and lowest in the middle. (Attraction Repulsion At The Poles)   From this it can be concluded that the attraction force of the magnet is highest on both the sides or lowest in the middle.  The two ends of the side of a magnet are called poles of the magnet.

2. Directional Property

If a magnet is tied with a thread and hung freely, then both its ends are always pointing in the north-south direction. The end which is towards the north is called the north pole of the magnet and the end which is towards the south is called the south pole.

The north pole of a magnet is represented by N and the south pole by S.

3. Attraction Repulsion At The Poles

If the north pole of one magnet is brought near the north pole of another magnet, then there is mutual repulsion between the two poles and if the north pole of a magnet is brought near the south pole of the other magnet then they mutually attract.

From this it can be concluded that there is repulsion between like poles of magnet and attraction between opposite poles.  An isolated pole does not exist.  When a magnet is broken from the middle, its poles do not separate, but the broken parts again become a complete magnet and north and south poles are generated in each part.

A lone charge can exist in a free state, but a lone magnetic pole cannot exist alone.  The line joining the north pole and south pole of a magnet is called the magnetic axis.

[What Is Magnetic Field | Properties Of Magnet]