subject: Electrical Devices In Industry [print this page] An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current.
The magnetic field disappears when the current is turned off. Electromagnet, Electromagnetic Devices, Solenoids and Lock Solenoids are widely used as components of other electrical devices, such as motors, generators, relays,scientific instruments, and magnetic separation equipment, as well as being employed as industrial lifting electromagnet for picking up and moving heavy iron objects like scrap iron.
An electric current flowing in a wire creates a magnetic field around the wire (see drawing below). To concentrate the magnetic field, in an electromagnet the wire is wound into a coil with many turns of wire lying side by side.
The magnetic field of all the turns of wire passes through the centre of the coil, creating a strong magnetic field there. A coil forming the shape of a straight tube (a helix) is called a solenoid a solenoid that is bent into a donut shape so that the ends meet is called a toroid. Much stronger magnetic fields can be produced if a core" of ferromagnetic material, such as soft iorn, is placed inside the coil. The ferromagnetic core increases the magnetic field to thousands of times the strength of the field of the coil alone, due to the high use of the ferromagnetic material. This is called a ferromagnetic-core or iron-core electromagnet.
Magnetic field produced by a(coil of fire). This drawing shows a cross section through the center of the coil. The crosses are wires in which current is moving into the page; the dots are wires in which current is moving up out of the page.
The direction of the magnetic field through a coil of wire can be found from a form. If the fingers of the right hand are curled around the coil in the direction of current flow (conventional current, flow) through the wings, the thumb points in the direction of the field inside the coil. The side of the magnet that the field lines emerge from is defined to be the north pole.
The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be rapidly manipulated over a wide range by controlling the amount of electric current. However, a continuous supply of electrical energy is required to maintain the field.
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