What is the difference between a permanent magnet and an electromagnet?
In an electromagnet the magnetic field is created through electric current in a wire-wound coil and strengthened by a soft-iron core.
As soon as you turn off the power, the soft-iron core loses its magnetisation.
A permanent magnet is made of ferromagnetic material, which is magnetised by a strong external magnetic field.
The magnetically hard material that is used keeps part of its magnetisation after the external magnetic field is turned off.
Note: We only carry permanent magnets in our shop, no electromagnets.
Table of Contents
Magnetic fields (B fields) in general
All magnetic fields (B fields) are created by electric charges or currents. Even a single charged electron produces a B field.Electromagnets
A wire with an electric current (charged electrons) produces a magnetic field in its surroundings.
The strength of the magnetic field depends on the intensity of the current and the shape of the wire.
Each wire with a current flow is practically an electromagnet.
The orange arrow indicates the technical direction of the current.
Historically, it is opposite of the direction of the electrons.
Coils
If you bend the wire with the current flow into a circle, it creates a magnetic field with poles (see picture). Therefore, a circulating current creates a magnet with a north and south pole.In common magnets the wire is often wound into a multi-layered coil, which is also called solenoid.
A wire coil with north and south pole
Soft-iron core (grey) with coil (orange)
Soft-iron core
When it comes to electromagnets, usually a soft-iron core is placed in the coil, which considerably strengthens its magnetic field, because the magnetic field of the coil magnetises the soft-iron core and, thereby, creates an additional magnet. The soft-iron core loses its magnetisation after the current is turned off. This is desirable in order to be able to turn the magnet on and off.Magnetically soft and hard iron
The term "magnetically soft" refers to the fact that mechanically soft iron loses its magnetisation, while carbon-enriched, mechanically hard iron (steel) keeps part of its magnetisation. This is called remanence. "Remanere" comes from the Latin "remain". Material with a high remanence is called "magnetically hard".Live solenoids are used to magnetise permanent magnets such as our super magnets, which are made of magnetically hard materials.
Permanent magnets
Electron with a spin: A microscopic magnet
Electron spins
In permanent magnets the B fields are also created through currents. But these currents are not macroscopic currents, in which charged particles flow in one direction. They are microscopic electric currents, which, in the case of ferromagnetism, are created through certain electrons rotating around themselves in the material (electron spins). An electron spin can be viewed as a microscopic small circulating current.Strengths of permanent and electromagnets
The strength of a magnetic field of an electromagnet depends on the core material, the number of solenoid windings and the intensity of the current. With a high enough amperage the electromagnet can develop a significantly stronger magnetic field than a permanent magnet.
Left: A permanent magnet with field lines
Right: An electromagnet with power source (left), solenoid (orange) and soft-iron core (middle)