Applications of the Electromagnet working

The Lifting Electromagnet

Large steel objects or scrap iron may be moved by lifting electromagnets.  A soft ferromagnetic core of high permeability is wound with copper wire.  Closing a switch to complete the circuit induces a very strong magnetic field in the soft iron core, strong enough to pick up iron and steel objects.  When the switch is opened, the magnetic field is instantly cut and objects attracted to the electromagnet are released.  Usually there are two cores used, wound in opposite directions to make the "legs" of the electromagnet opposite poles, doubling the strength of the electromagnet.

The Electromagnetic Relay

A relay is a switch that turns an electric current on or off.  The relay is operated by an electric current in a different circuit.  A pivoted bar of iron, called an armature, is held clear of the contact point by a spring.  No current flows through the lamp's circuit.  When the switch is closed, the magnetized iron core attracts the armature, closing the circuit and lighting the lamp.

The Electric Bell

In an electric bell, a small hammer is attached to the armature.  The armature is vibrated back and forth so that the hammer repeatedly hits the gong.  The circuit is similar to the electromagnetic relay, except there is only one circuit.  When the switch is closed, the iron core becomes magnetized and attracts the armature, ringing the bell.  However, the movement of the armature breaks the circuit and demagnetizes the core, and the spring returns the armature to its original position, again completing the circuit and remagnetizing the core.  The process is then repeated.

The Telephone Receiver

Where you speak into a telephone, a microphone is used to convert sound energy into electrical energy.  The telephone receiver converts electrical energy into sound energy.

In the receiver, there is a permanent magnet attached to two solenoids.  When current flows through the coils, an iron diaphragm is attracted to the coils.  If the current is varied, the diaphragm moves in and out.  It alternately compresses, or rarefies, the air between it and a plastic case, producing sound waves.

Magnetic Recording Tapes and Disks

A recording tape or disk is made by coating a non-magnetic substance, like plastic, with a very thin layer of a material containing millions of magnetic particles.  This coating is typically iron oxide.  Pulses of electric current are sent to the "write head," an electromagnet with a soft iron core and a small air gap.

When a magnetic field is set up in the core, the magnetic field passes through the magnetic layer of the tape or disk at the location of the air gap.  The tape is moved rapidly past the air gap, and its magnetic domains are aligned according to the signals received from the core.  The domain arrangement stores the information.

To retrieve the stored information, a "read head" resembling the write head reads the tape as it is passed over it.  The domains on the tape control the input of current in the coil of the read head and the current is interpreted by the computer or stereo.