Magnetism

# Magnetic Field

The space around a magnet in which its magnetic force can be realised is called magnetic field. Theoretically, magnetic field is extended upto infinity although practically we consider it only upto certain distance.

## Magnetic Field Lines

Magnetic field lines are the hypothetical closed curves through which a unit north pole would move if it were free to move and tangent at every point of the curve gives the direction of the resultant magnetic field.

## Properties

1. Magnetic field lines come out from North pole and enter the South pole but these lines go from South pole to North pole inside the magnet at any angle.
2. They are continuously closed curves.
3. They repel each other laterally (sideways) so there is repulsion between similar poles.
4. They are like stretched elastic thread which tend to contract along their lengths so there is attraction between unlike poles.
5. These lines never cross each other. If they cross each other, then at the point of intersection there will be two tangents which will show two directions of magnetic field. But magnetic field is a vector quantity, so it should not have two directions. Hence, two magnetic field lines never intersect each other.
6. They are affected by earth’s magnetic field.
7. Tangent at any point to magnetic field lines gives the direction of magnetic intensity at that point.
8. Increment in magnetic field lines increases the strength of magnetic field.

A magnetic field can be represented by a set of magnetic field lines. If the lines are close to each other, then it represents strong field and if the lines are spaces widely apart, it represents weak field. There are two types of magnetic field; uniform magnetic field and non uniform magnetic field.

## Uniform Magnetic Field

A magnetic field in which magnetic intensity is same at all the points is called a uniform magnetic field. It is an ideal situation, this type of magnetic field is not possible. Hence, a magnetic field in which magnetic intensity is nearly equal (in both magnitude and direction) is called uniform magnetic field. An example of uniform magnetic field is earth’s magnetic field. It is represented by a set of parallel lines of force.

## Non-uniform Magnetic Field

A magnetic field in which magnetic intensity is different at different points is called a non-uniform magnetic field. It is represented by a set of convergent, divergent or curved lines of force.

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