What Is The Magnetic Field Around A Bar Magnet: Exhaustive Facts On Various Objects


In this article, we are going to see what is the magnetic field around a bar magnet and Where is the magnetic field of a bar magnet strongest.

The magnetic field caused by the presence of the bar magnet is extreme at the edges of the poles and is very poor at the middle of the bar magnet.

What is a Bar Magnet

A magnet appearing like a bar, and hence called a bar magnet has two poles, the poles of the bar magnet are protected from demagnetizing the magnet using iron plates on both the poles.

A bar magnet is composed of ferromagnetic material that retains its magnetic properties even in the absence of an external field and hence is a permanent magnet.

On hanging freely in the air, the bar magnet aligns itself in the North-south direction. The magnetic dipoles inside the bar magnet experience the magnet force due to the Earth’s magnetic field and align in the direction of the field. Hence, a bar magnet can therefore be used to find the direction same as a compass.

Types of Bar Magnet

There are two types of the bar magnet, they are:-

1) Rectangular bar magnet: This magnet has four rectangular faces painted and two square shape poles. The edges of this bar magnet are rectangular in shape and hence the name rectangular bar magnet.

Rectangular Bar Magnets; Image credit: mfidie

2) Cylindrical bar magnet: The edges of the magnet are circular and therefore called cylindrical bar magnets. The outer curvature of this magnet is coloured.

Cylindrical Bar Magnets;
Image credit: hsmagnets

Where is the Magnetic Field of a Bar Magnet Strongest and Why

The magnetic field is strongest at the edges of the poles of the bar magnet.

If we take a simple example that we probably have performed as the first experiment at schools when were introduced about the magnetic field, an experiment with a bar magnet and an iron foils. The bar magnet when placed in a tray of iron foils, the iron foils are arranged around the bar magnet in well-aligned concentric circles without overlapping.

magnetic field
Magnet field by a bar magnet;
Image credit: comnewsscience

The majority of the irons are gathered near the North and the South poles of the bar magnet. This is because; the magnetic field lines are originating from the poles. The strength of the field weakens drastically as the distance from the poles widens.

Secondly, the bar magnet actually acts as a dipole, the negative and positive particles spin are aligned according to the magnetic field of the Earth. Dipoles themselves behave like a small tiny magnet. Even if we cut the bar magnet further into pieces, it will show the same behavior forming two poles of the opposite charges like a bar magnet.

The magnetic dipoles in the magnet will always align themselves as per the magnetic field. The positive and negative spins will try to align towards the poles of the bar magnet thus intensifying the strength of the magnetic fields at the poles.

Where is the Magnetic Field of a Bar Magnet Weakest

If we look into the same experiment as mentioned above; we shall see, there are hardly any iron foils attached on the middle portion of the bar magnet, nor you will find any field lines originating from this part of the magnet and are almost parallel to the length of the bar magnet.

Also, it is been observed that the magnetic field lines which are running parallel to the length of the bar magnet are separated from each other making a gap that widens every loop. While at the poles, the magnetic lines are more densely without forming any gap.

The magnetic field strength of the bar magnet through intense at the poles will start faltering as the distance between the poles increases.

The tiny dipoles inside the bar magnet always align themselves in the direction of the Earth’s magnetic field, hence the spins are oriented towards each pole.

The parallel aligned dipoles show both attraction and repulsion thus neutralizing the effect of the magnetization; there is a presence of a magnetic field but comprises weaker strength of the field. In consequence, diminishing the magnetic field at halfway from the poles of the bar magnet.

Is a Bar Magnet Surrounded by a Magnetic Field

The dipoles inside the ferromagnetic material of what the bar magnet is comprising of, possesses the magnetic dipole moments which are responsible for the generation of a magnetic field of a bar magnet. Being a permanent magnet, it will attract ferromagnetic materials towards it, while showing some force of attraction or repulsion on other magnetizing material when placed near the bar magnet and not too far.

The magnetic force around the bar magnet will act only when the substance is placed in its field. Outside the magnetic field of the bar magnet, evidently, the strength of the field is zero as there are no magnetic flux lines flowing in this region.

Being magnet will show some forces of attraction and repulsion in an area surrounded by it, this implies that the magnetic field does occur around the magnet, which is represented as a magnetic flux oriented in concentric circles, beyond this range of magnetic field; no effect of the magnet is observed.

How to Draw Magnetic Field Lines Around a Bar Magnet

The magnetic field lines are represented as the flux lines. These flux lines form concentric closed loops. The magnetic field produced by the bar magnet is represented by flux lines that are originating from one pole and terminate into another pole of the bar magnet.

Hence, the magnetic field lines can be drawn originating from the North Pole and entering in the South pole forming close loops, and these loops are separated from one another at a certain distance while running parallel to the length of the bar magnet and this gap widens for every loop, on the contrary, the magnetic lines are drawn dense at the poles.

No magnetic field lines should touch the middle section of the bar magnet as the magnetic field is negligible in this area and has a weak force of attraction or repulsion.

What is the Direction of Magnetic Field Lines Outside a Bar Magnet

what is the magnetic field around a bar magnet
Magnetic field direction; Image credit: teachoo

The magnetic field of the bar magnet is due to the presence of the dipole. The positive and the negative charges of a particle separated by a small distance due to some external field applied is called a dipole. These dipoles are line-up in accordance with the magnetic field. Hence, in absence of a magnetic field, the dipoles inside the bar magnet are positioned as per the Earth’s magnetic field. This orientation of the dipoles inside the bar magnet is then responsible for the direction of the magnetic field lines generating outside the bar magnet.

The dipoles are aligned parallelly in the direction from the South Pole to the North and hence the direction of the magnetic field lines outside a bar magnet are arising from the North pole to the South.

Is the Magnetic Field Same all Around a Bar Magnet

The magnetic field depends upon the strength and density of the magnetic flux lines and varies with respect to the distance from the poles. The intensity of the magnetic field is directly proportional to the magnetic flux density. The flux density varies with distance.

The magnetic field produced by the bar magnet is at a peak near the edges of the poles. The weak force of attraction and repulsion is experienced at the middle part of the bar magnet.

The reason why I am considering both attraction and repulsion in the middle portion of the bar magnet is due to the fact that the dipoles are arranged across the length of the bar magnet are parallel to the magnetic flux lines in the region outside the magnet, the dipole itself behaves like a tiny magnet.

The parallelly aligned dipoles show the force of attraction as well as repulsion from two different ends of the dipole depending upon the orientation of the spin of the charge. This results in neutralizing the effects of pulling and pushing away and weakens the magnetic field strength.

Thus the magnetic field strength is highest at the edges of the poles of the magnet. The strength decreases as the distance from the poles across the length of the bar magnet increases. The same is the effect around the bar magnet. As the distance from the magnetic poles increases the strength of the field will also decrease as we go far from the poles.

Magnetic Force Imposed by the Bar Magnet on Various Objects

The bar magnet will show the force of attraction when the ferromagnetic materials like objects made up of iron, steel, or an alloy of irons are brought in closer contact with the magnet.

Whereas, it will show repulsive forces when comes in contact with the substances having diamagnetic characteristics; for example, mercury, water; and will experience the weak force of attraction with objects like aluminum, tungsten, etc. which are paramagnetic substances.

Read more on Magnetic Field Vs Magnetic Field Strength: Different Aspects and Facts

 

Frequently Asked Questions

If the bar magnet of length 10cms kept on a table experience the magnetic strength 30 cms away from the magnet, then calculate the magnetic field strength of the bar magnet. The horizontal component of the Earth field is 0.34G.

Given:-

Horizontal component of the Earth

BH=0.34G=0.34*10-4

2l= 10cms; => l=5cm=0.05m

t=30cms = 0.30m

Neutral point is obtained on the axial line.

Baxial=BH

[

[0.34*103*(0.0875)2]/(2*0.30)

=4.34Am2

Hence the strength of the magnetic poles of the bar magnet is

m=M/2I=4.34/10=0.434Am

What are the different uses of bar magnets?

A bar magnet is used for various purposes may be industrial, electronics, chemical industries, laboratories, etc.

The bar magnet is used to separate magnetic substances from the heap of mixtures, for stirring the chemical mixture to facilitate the movement of the magnetic substance, in electronic devices like TV, microphones, mobiles, etc.; it is used as a small chip in the electronic devices.

Why does bar magnet have the North Pole and the South Pole?

When the bar magnet is suspended in the air, it will continuously show harmonic motion until it gets aligned in the direction of the Earth’s magnetic field.

Due to the separation of charges inside the magnet, one end of the bar magnet becomes more positive and the other is more negative. The magnetic dipoles inside the bar magnet experience the Earth’s magnetic force and are aligned with respect to the Earth’s magnetic field. The magnet has two poles same as the Earth, and in a free suspended position in the air, it will align with respect to the Earth’s magnetic field that is in the north-south direction. Hence, the names the North and the South pole to two different poles of a bar magnet.

Does the magnet work in space?

Yes. The magnet can be used in space even in the absence of an atmosphere.

As the magnetizing dipole field inside the magnet is permanent and zero work is required to build the magnetic field around the magnet, it will definitely work in space as well.

Read more about Magnetic Field Lines Around A Magnet.

AKSHITA MAPARI

Hi, I’m Akshita Mapari. I have done M.Sc. in Physics. I have worked on projects like Numerical modeling of winds and waves during cyclone, Physics of toys and mechanized thrill machines in amusement park based on Classical Mechanics. I have pursued a course on Arduino and have accomplished some mini projects on Arduino UNO. I always like to explore new zones in the field of science. I personally believe that learning is more enthusiastic when learnt with creativity. Apart from this, I like to read, travel, strumming on guitar, identifying rocks and strata, photography and playing chess. Connect me on LinkedIn - linkedin.com/in/akshita-mapari-b38a68122

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