Electromagnet vs Permanent Magnet
Electromagnets and permanent magnets are two important topics in electromagnetic theory. This article will explain the fundamentals of magnetism, electromagnet and permanent magnet and describe the between the two magnets.
What is Electromagnet?
To understand electromagnets, one must first understand the theories behind magnetism. Magnetism occurs due to electric currents. A straight current carrying conductor exerts a force, normal to the current, on another current carrying conductor placed parallel to the first conductor. Since this force is perpendicular to the flow of charges, this cannot be an electric force. This was later identified as magnetism.
The magnetic force can be either attractive or repulsive but always mutual. A magnetic field exerts force on any moving charge, but stationary charges are not affected. A magnetic field of a moving charge is always perpendicular to the velocity. The force on a moving charge by a magnetic field is proportional to the velocity of the charge and the direction of the magnetic field.
一个磁铁两极。他们被定义为North Pole and South Pole. The magnetic field lines start in the North Pole and end in the South Pole. However, these field lines are hypothetical. It must be noted that magnetic poles does not exist as a monopole. The poles cannot be isolated. This is known as the Gauss’ law for magnetism. An electromagnet is a component made up of current carrying loops. These loops can be of any shape, but common electromagnets have the shape of solenoids or rings.
What is Permanent Magnet?
由于电流是唯一的方法来创建一个magnet, permanent magnets must consist of currents. Every atom has electrons orbiting the nucleus of the atom, and these electrons have a property called the electronic spin. These two properties are responsible for the magnetism in materials. Materials can be grouped into several categories according to their magnetic properties. Paramagnetic materials, Diamagnetic materials, and Ferromagnetic materials are to name a few. There are also some lesser common types such as anti-ferromagnetic materials and ferrimagnetic materials. Diamagnetism is showed in atoms with only paired electrons. The total spin of these atoms is zero. The magnetic properties arise only due to the orbital motion of electrons. When a diamagnetic material is placed in an external magnetic field, it will produce a weak magnetic field anti-parallel to the external field. Paramagnetic materials have atoms with unpaired electrons. The electronic spins of these unpaired electrons act as small magnets, which are stronger than the magnets created by the electron orbital motion. When placed in an external magnetic field, these small magnets align with the field to produce a magnetic field, which is parallel to the external field. Ferromagnetic materials are also paramagnetic materials with zones of magnetic dipoles in one direction even before the external magnetic field is applied. When the external field is applied, these magnetic zones will align themselves parallel to the field so that they would make the field stronger. Ferromagnetism is left in the material even after the external field is removed, but paramagnetism and diamagnetism vanishes as soon as the external field is removed. The permanent magnets are made up of such ferromagnetic materials.
What is the difference between electromagnets and permanent magnets? • Permanent magnets are also electromagnets with a continuous current flowing, making every atom a magnet. • Electromagnetism disappears once the external current is stopped, but the permanent magnetism remains. |
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