History and Applications of Electromagnets
– Danish scientist Hans Christian Ørsted discovered electric currents create magnetic fields in 1820.
– French scientist André-Marie Ampère showed that iron can be magnetized by inserting it in an electrically fed solenoid in 1820.
– British scientist William Sturgeon invented the electromagnet in 1824.
– Sturgeon’s first electromagnet was a horseshoe-shaped piece of iron wrapped with about 18 turns of bare copper wire.
– US scientist Joseph Henry improved and popularized the electromagnet starting from 1830.
– Electromagnets are used in motors, generators, transformers, relays, electric bells and buzzers, loudspeakers, and headphones.
Basics of Electromagnets
– An electric current creates a magnetic field around a wire.
– The wire is wound into a coil to concentrate the magnetic field.
– The magnetic field passes through the center of the coil, creating a strong magnetic field there.
– The direction of the magnetic field inside the coil can be determined using the right-hand rule.
– A solenoid is a coil forming the shape of a straight tube.
Magnetic Core and Magnetic Circuit
– A magnetic core, often made of iron or steel, is composed of small regions called magnetic domains.
– When a current is passed through the wire wrapped around the core, the domains align parallel to the magnetic field, creating a large magnetic field.
– The core concentrates the magnetic field and allows it to pass through more easily than air.
– In practical applications of electromagnets, the iron core is often in the form of a loop or magnetic circuit with air gaps.
– The magnetic field lines form closed loops, and most of the field’s path is within the core to obtain a stronger field.
– Leakage flux refers to field lines that do not pass through the entire core circuit and do not contribute to the force exerted by the magnet.
Nonlinear Features of Ferromagnetic Materials
– Ferromagnetic materials have a nonlinear relationship between magnetic field (B) and magnetizing field (H).
– The B field saturates at a certain value, typically around 1.6 to 2 teslas (T) for high permeability core steels.
– Hysteresis occurs when some alignment of domains persists even after the current is turned off, creating remanent magnetism.
– Degaussing can remove the residual magnetization of the core.
Magnetic Field Strength and Force Exerted
– The maximum strength of the magnetic field from an iron core electromagnet is limited to around 1.6 to 2 T.
– The permeability of free space (or air) is represented by μ0=4π(10^-7) N·A^-2.
– The force exerted by an electromagnet on a section of core material is given by F = B^2A / (2μ0).
– In a closed magnetic circuit (no air gap), the magnetic field (B) is given by B = (NIμ) / L.
– The force exerted in a closed magnetic circuit is given by F = (μ^2N^2I^2A) / (2μ0L^2).
– The force between two electromagnets can be found using the magnetic-charge model. Source: https://en.wikipedia.org/wiki/Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.
The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field.
Electromagnets are widely used as components of other electrical devices, such as motors, generators, electromechanical solenoids, relays, loudspeakers, hard disks, MRI machines, scientific instruments, and magnetic separation equipment. Electromagnets are also employed in industry for picking up and moving heavy iron objects such as scrap iron and steel.
