Magnetic field Due to a Current Carrying Conductor

These notes are based on the chapter Magnetic Effect of Electric current class 10 science NCERT book and CBSE syllabus.

Magnetic field due to current through a straight conductor

A current carrying straight conductor has magnetic field in the form of concentric circles around it. Magnetic field of current carrying straight conductor can be shown by magnetic field lines.

The direction of magnetic field through a current carrying conductor depends upon the direction of flow of electric current. The direction of magnetic field gets reversed in case of a change in the direction of electric current.

Let a current carrying conductor be suspended vertically and the electric current is flowing from south to north. In this case, the direction of magnetic field will be anticlockwise. If the current is flowing from north to south, the direction of magnetic field will be clockwise.

The direction of magnetic field, in relation to direction of electric current through a straight conductor can be depicted by using the Right Hand Thumb Rule. It is also known as Maxwell’s Corkscrew Rule.

Right Hand Thumb Rule

If a current carrying conductor is held by right hand, keeping the thumb straight and if the direction of electric current is in the direction of thumb, then the direction of wrapping of other fingers will show the direction of magnetic field.

In this figure, direction of thumb is upwards and direction of other fingers' wrapping is counter-clockwise. This means that direction of current is upwards, and direction of magnetic field is counter clockwise when seen from above.

Maxwell's Corckscrew Rule

As per Maxwell's corkscrew rule, if the direction of forward movement of screw shows the direction of current, then the direction of rotation of screw shows the direction of magnetic field.

In this figure, the screw is moving downwards and in clockwise direction. So, direction of electric current is downwards, and direction of magnetic field is clockwise when seen from above.

Properties of Magnetic Field

The magnitude of magnetic field increases with increase in electric current and decreases with decrease in electric current. This means that magnetic effect will increase if amount of current through the conductor is increased. This also means that magnetic effect will decrease if amount of current through conductor is decreased.
The magnitude of magnetic field, produced by electric current, decreases with increase in distance and vice-versa. The size of concentric circles of magnetic field lines increases with distance from the conductor, which shows that magnetic field decreases with distance. This means that if a magnetic object is kept near the current-carrying conductor, the object would experience a greater magnetic force than when it is kept far from the conductor.
Magnetic field lines are always parallel to each other.
No two field lines cross each other.