What are Magnets?

It is a material or an object which produces a magnetic field. Magnets consist of the south pole and the north pole. This field is invisible but is responsible for the most notable property of a magnet. A magnetic force pulls other ferromagnetic materials such as iron, steel, nickel, cobalt, etc. They attract and repel other magnets.

Physics behind magnets magnetic field

the magnetic flux density is a vector field. The magnetic B field vector at a given point in space is specified by two properties:

  1. Its direction, which is along with the orientation of a compass needle.
  2. Its magnitude is proportional to how strongly the compass needle orients along that direction.

Magnetic moment

A magnet’s moment is a vector that characterizes the magnet’s overall magnetic properties. For a bar magnet, the direction of the magnetic moment points from the magnet’s south pole to its north pole. The magnitude relates to how strong and how far apart these poles are.A magnet both produces its own magnetic field and responds to magnetic fields. The strength of the magnetic field it produces is at any given point proportional to the magnitude of its magnetic moment. In addition, when the magnet is put into an external magnetic field, produced by a different source, it is subject to a torque tending to orient the magnetic moment parallel to the field. 

The amount of this torque is proportional both to the magnetic moment and the external field. A magnet may also be subject to a force driving it in one direction or another, according to the positions and orientations of the magnet and source. If the field is uniform in space, the magnet is subject to no net force, although it is subject to a torque.

Magnetization

magnetic field 
magnets
the north pole
the south pole
pole

The magnetization of a magnetized material is the local value of its magnetic moment per unit volume, usually denoted M, with units A/m. It is a vector field, rather than just a vector (like the magnetic moment), because different areas in a magnet can be magnetized with different directions and strengths (for example, because of domains, see below). A good bar magnet may have a magnetic moment of magnitude 0.1 A·m2 and a volume of 1 cm3, or 1×10−6 m3, and therefore an average magnetization magnitude is 100,000 A/m. Iron can have a magnetization of around a million amperes per meter. Such a large value explains why iron magnets are so effective at producing magnetic fields.

Modeling magnets

magnetic field 
magnets
the north pole
the south pole
pole

Two different models exist for magnets: magnetic poles and atomic currents.

Although for many purposes it is convenient to think of a magnet as having distinct north and south magnetic poles, the concept of poles should not be taken literally: it is merely a way of referring to the two different ends of a magnet. The magnet does not have distinct north or south particles on opposing sides. If a bar magnet is broken into two pieces, in an attempt to separate the north and south poles, the result will be two bar magnets, each of which has both a north and south pole. However, a version of the magnetic-pole approach is used by professional magneticians to design permanent magnets.

In this approach, the divergence of the magnetization ∇·M inside a magnet and the surface normal component M·n is treated as a distribution of magnetic monopoles. This is a mathematical convenience and does not imply that there are actually monopoles in the magnet. If the magnetic-pole distribution is known, then the pole model gives the magnetic field H. Outside the magnet, the field B is proportional to H, While inside the magnetization must be added to H. An extension of this method that allows for internal magnetic charges is used in theories of ferromagnetism.

Further continuing..

Another model is the Ampere model, where all magnetization is due to the effect of microscopic or atomic, circular bound currents. also called Ampèrian currents, throughout the material. For a uniformly magnetized cylindrical bar magnet, the net effect of the microscopic bound currents is to make the magnet behave as if there is a macroscopic sheet of electric current flowing around the surface, with local flow direction normal cylinder axis. Microscopic currents in neighboring atoms.

Polarity

The north pole of a magnet is defined as the pole that, when the magnet is freely suspended, points towards the Earth’s North Magnetic Pole in the Arctic. Since opposite poles (north and south) attract, the North Magnetic Pole is actually the south pole of the Earth’s magnetic field. As a practical matter, to tell which pole of a magnet is north and which is south, it is not necessary to use the Earth’s magnetic field at all.

Types of permanent magnets

  • Magnetic metallic elements

Many materials have unpaired electron spins, and the majority of these materials are paramagnetic. When the spins interact with each other in such a way that the spins align spontaneously, the materials are called ferromagnetic. Because of the way their regular crystalline atomic structure causes their spins to interact, some metals are ferromagnetic when found in their natural states, as ores.

  • Composites

Ceramic, or ferrite, magnets are made of a sintered composite of powdered iron oxide and barium carbonate ceramic. Given the low cost of materials and manufacturing methods.


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