The Concept of Bar Magnet

A bar magnet is a rectangular or cuboidal-shaped permanent magnet that attracts objects like iron and steel of iron. Magnets have two poles, the north pole and the south pole. When a bar magnet is freely suspended, then its north pole will point towards the geographical north, and the south pole will point towards the geographical south pole. When you place two bar magnets against each other, the opposite poles will attract, and similar poles will repel each other. 

Properties of a bar magnet:

• Magnetic field lines: The magnetic field line is an abstract structure that defines the influence of magnetic forces. The magnetic field lines are visuals and intuitive realisation of the magnetic field. The larger the number of field line crossings per unit area, the stronger the magnitude of the magnetic field. 

• Magnet is the material present in this world to get attracted or repelled by their object, and it produces a magnetic field around it. Let us look at the poles and how they are attracted and repelled by their object.

• South-South (repel each other).

• North-South (attracts each other).

• South-North (attracts each other).

• North-North (repel each other).

• Magnet poles can not be isolated because they are always found in bipolar form. Even if we want, we cannot isolate these magnets by cutting them into two pieces. Each magnet has its north pole and south pole.

Bar magnet as an equivalent solenoid: 

A solenoid can behave like a magnet if an electric current passes through it; thus, it is an electromagnet. Now let us consider if a solenoid splits into two pieces, what would happen? Both solenoid parts will continue behaving like magnets with a weaker magnetic field. Eventually, electricity and magnetism are correlated to each other. That is why together, their fields  (ie, electric and magnetic fields) are known as electromagnetism. Let us consider the magnetic dipole moment ‘m’ associated with the current loop expressed as 

m = NIA.

Here,

N = number of turns in the loop,

I = Electric current, and 

A = Area vector

Bar magnet in different states: 

Like matter, which is present in every state, a magnet can also be present in every state. Neodymium magnet is found in the solid state, ferrofluids are found in the liquid state, and strong magnetic properties are not seen in the gaseous state. In the gaseous state, ferromagnetic material is absent while paramagnetic material can be found.

The dipole in a uniform magnetic field: 

In this paragraph, we will study the nature of forces acting on a dipole that is kept in a uniform magnetic field. This is done by placing a magnetic rod in a uniform magnetic field, then the north pole of the rod experiences a force that is equal to the multiplication of the magnetic field intensity to the pole strength in the magnetic field’s direction. The south pole also experiences a force equal in magnitude but opposite in direction. Hence a torque exerts on both sides of the pole, due to which the rod starts rotating.

The torque on the rod is expressed as,

=mB

In terms of magnitude, it is expressed as

Ꞇ = mB sin

Here, 

Ꞇ is the restoring torque, 

m is the magnetic dipole,

B is the external magnetic field in which magnetic dipole is placed, and

  is the angle between m and B.

The dipole analogy: 

The analogy is the comparison between one thing and another. Here we are discussing electric fields and magnetic fields. Take a look at the table for more clarification about electrostatics and magnetism.

                                    

Conclusion

This article explains the concept of a bar magnet. A bar magnet is a rectangular or cuboidal-shaped permanent magnet that attracts objects like iron and steel of iron. When you place two bar magnets against each other, the opposite poles will attract, and similar poles will repel each other. A solenoid can behave like a magnet if an electric current passes through it. A Bar magnet is a permanent magnet, whereas a solenoid is an electromagnet. Bar magnets are not affected by electric current, but solenoids are affected by electric current.