Magnetic effect of current:

Magnetic field: The space around a magnet within which its influence can be experienced is called its magnetic field.

A moving charge or a current sets up or create a magnetic field in the space surrounding it.

The magnetic field exerts a force on a moving charge or a current in the field:

Oersted’s Experiment: Consider a magnetic needle SN pivoted over a stand. Hold a wire AB parallel to the needle SN and connect it to a cell and a plug key as shown in fig.

It is observed that:

1)      When the wire is held above the needle and the current flows from south to north, the north pole of the magnetic needle gets deflected towards the west, as shown in fig.

2)      When the direction of the current is reversed, so that it flows from the north to the south, the north pole of the magnetic needle gets deflected towards the east, as shown in fig.

3)      When the wire is placed below the needle, the direction of deflection of the needle is again reversed.

4)      When the current in the wire is stopped flowing, the magnetic needle comes back into its initial position.

Ampere’s Swimming Rule: This rule predicts the direction of deflection of the magnetic needle in the Oersted’s experiment, it can be stated as follows:

“Imagine a man swimming along the wire in the direction of the current with his face always turned towards the magnetic needle, then the north pole of the needle will get deflected towards his left hand”.

It is also known as “SNOW”. It indicate that if the current flows from south to north and the wire is held over the needle, the north pole is deflected towards the west.