Magnetic Flux

If we place an imaginary isolated north pole in a magnetic field, it will experience a repulsive force from the north pole and an attractive force from the south pole of the magnet. These forces will cause the north pole to move along a specific path if it is free to do so. Placing the north pole at different distances from the magnet may result in different paths.

These paths of the unit north pole in the field are called lines of force. Since the north pole can be placed at an infinite number of points in the field, there can be infinite lines of force. However, visualizing infinite lines is impractical for calculations. To represent the strength of a magnetic field, we use the unit of magnetic flux, called the weber. If a field has φ weber flux, it means it has φ lines of force. Like the isolated north pole, lines of force are imaginary and used for calculations and explaining magnetic properties.

Properties of Magnetic Flux

1. Magnetic flux of a filed is considered as the total number of magnetic lines of force in the field. These are also called magnetic flux lines.
2. Each magnetic flux line is closed loop.
3. Each magnetic flux line starts from north pole of a magnet and comes to the south pole through the field and continues from south pole to north pole in the body of the magnet.
4. No two flux lines cross each other.
5. Two similar lines of force travel side by side but repeal each other.
6. The lines of force are stretched like elastic cord.

Magnetic Flux Density

The number of magnetic lines of force passing through a unit area surface perpendicular to the magnetic field is called magnetic flux density.

If total φ Weber flux passes perpendicularly through a surface area of A m², the magnetic flux density of the field is,

We generally represent magnetic flux density with the capital letter B.