Magnetism And Electromagnetism » Electro-magnets

Electro-Magnets

When a current flows through a conductor, a magnetic field is generated around the conductor. This was discovered by a Danish scientist named Oersted in 1819. The iron filings form a definite pattern of concentric rings around the conductor is shown in the figure below. This indicates that the magnetic field is produced in the wire.

FIGURE

        The rotation direction of this magnetic field is controlled by the direction of the current flow through the conductor. Also the strength of the magnetic field highly depends on the amount of current as shown in the figure below.

FIGURE

 

Magnetic Rules

Corkscrew rule: The direction in which the corkscrew moves is the direction of current flow in the conductor, as shown in the figure below. This corkscrew rule helps in remembering the magnetic field direction, which forms around the conductor.

FIGURE

Right hand grip rule: In this rule, the conductor is grasped in such a way that the thumb points along the direction of current and the fingers in the direction of the flux lines as shown in the figure below.

FIGURE

        As you can see in the figures below, in the clockwise field, the current is flowing into the paper, which is represented by a cross mark in the middle. Whereas in the anticlockwise field, the current is flowing away from the paper, which is represented by a dot mark.

FIGURE

        When using two conductors, the attraction and repulsion depends on the direction of the current flow. The rules of superposition of magnetic fields are as follows.

  • If the direction of the current is the same, the magnetic field overlap and form one large magnetic field, as shown in the figure below.

FIGURE

  • If the direction of the current is opposite, then repulsion takes place between the wires, as shown in the figure below.

FIGURE

        Solenoid is used to obtain a stronger magnetic field from a conductor. It is a coil wound into a tightly packed helix, which will increase the magnetic effect. When a direct current is passed through the solenoid, the addition of each twisting in the coil produce a stronger effect.