# What Produces the Strength of a Magnetic Field: Different Methods and Facts

In this article, we are going to discuss what produces the strength of a magnetic field and the different factors responsible for its formation.

What produces the strength of the magnetic field is the magnetic flux passes through a unit length of the conductor and increases as the flux density per unit length increases.

## Magnetic Field and It’s Intensity

Let us now see different methods and some facts of a magnetic field.

First of all, do you all know how the magnet was discovered?

A shepherd called Magnas who lived in Greece used to carry a stick along with him to control the herd of sheep and goats which had an iron underneath which stuck to the rock. The rock was a natural magnet, rich in iron (Fe content) called Magnetite. Hence the discovery of the magnet took place in Greece and now that place is called Magnesia, a name based on the discovery of magnet.

As the magnetic field strength of the Earth is greatest at the North pole and the South pole, the magnet is always aligned in the North-South direction and hence is used to locate the direction by sea ventures. Especially, clinometers are used to measure the angle of elevation of the rocks by most geologists.

## What produces the strength of a Magnetic Field

Magnetic field strength is a force needed to generate a flux density in a material per unit length of the material and represented as:

H=(B/μ)-M

Where B is a magnetic flux density,
M is magnetization and
m is magnetic permeability.

$H= \frac{B}{\mu}-M \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ …………Eq.(1)$
Where B is a magnetic flux density,
M is magnetization and
m is magnetic permeability.

Magnetic strength depends on the total magnetic field lines which are pervasive through the total cross-sectional area of the material. These magnetic field lines are known as magnetic flux, and the density of the magnetic flux is directly correlated to the strength of the field. The magnetic flux density primarily depends upon the number of electron spins or the dipole moment in the material.

In an atom, electrons are found paired with electrons with opposite spin and it is usually found in the case of noble gases elements which have complete outmost valence shell and all electrons are paired with each other; an example of such elements are Helium, Neon, Argon, Krypton, Xenon, Radon.

Atoms that have unpaired electrons pair with electrons from the other atom to complete their outer shell and become a stable element. Those atoms with unpaired electrons yield a magnetic field. The unpaired electron revolves around the nuclei of the atom and the motion of the free electrons influences the origination of the magnetic field. As the number of available free electrons increases, the magnetic effects seen in the material will also escalate.

When current is passed through any conductor, the motion of electrons takes place that induces electromagnetic force. Suppose, you take a wire-carrying current, and place a magnetic needle near it, then you will identify the deflection of the magnetic needle. This is because the moving electrons in the current-carrying conductor produce a magnetic field in the direction that opposes the motion of the electrons.

As per the right-hand thumb rule, if the motion of current is from south to north direction then the magnetic field will be clockwise and the magnetic force will be experienced in the west direction. If we move the magnetic needle away from the current-carrying wire, the same effect will get diminished as the distance between the wire and the magnetic needle increase. Hence we can note that the magnetic field strength decreases along with the distance.

Magnetic field strength also depends upon the intrinsic magnetic moment of the particle. The magnetic moment is a quantity that determines the torque experienced by the dipoles in the presence of the external magnetic field.

In absence of a magnetic field, magnetic moments are oriented randomly and no net magnetization is produced; when the magnetic field is applied these atomic moments orient themselves in the direction of the applied field which results in the net magnetization parallel to the applied field. Hence, magnetization depends upon the density of the magnetic moment in the material, motion of electrons in the atoms, and the spin of the electron or the nuclei and defines as a magnetic moment per unit volume of a solid.

The strength of the magnetic field also depends upon the magnetic moment set up per unit volume of the material in the presence of an external field is known as magnetic susceptibility.

Based on this property, materials are classified into diamagnetic, paramagnetic, or ferromagnetic. It is known that ferromagnetic material has high magnetic susceptibility because it shows high magnetic properties and retains its magnetic properties even in the absence of an external magnetic field. Iron, nickel, cobalt are some of the ferromagnetic materials.

Moving electrons in the magnetic field experience the force which is perpendicular to its own velocity and magnetic force B is represented as:

F=qvB

Where q is a charge
v is the velocity of the charge
B is a magnetic field

$F=qvB \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ……….Eq.(2)$
Where q is a charge
v is the velocity of the charge
B is a magnetic field

The property of the material to repel the magnetic flux through it is called magnetic permeability. The material is said to have high permeability if the maximum magnetic flux passes through it.

## SI Unit of Magnetic Field Strength

Magnetic flux density is measured as a flux per unit area that is Weber/ m2 which is equal to one Tesla. Or we can say, it is measured in terms of the force required to induce magnetic flux in a unit length in meter per unit Ampere and given as N/A.m.

SI unit of magnetic susceptibility is given as Newton per ampere square N/A2 and that of magnetization is represented as Ampere per meter A/m. Substituting this in eq.(1), we get:

(N/A.m)*(A2/N)=(A/M)

$\frac{N}{A.m}\times \frac{A^{2}}{N}=\frac{A}{m}$

Based on this, we get the SI unit of magnetic field strength as Amperes per meter. In the CGS unit, it is Oersted, named after the Danish scientist Hans Christian Oersted who first found the relation between electricity and magnetism.

The intensity of the magnetic field is measured using a magnetometer. Induction magnetometer, rotating coil magnetometer, Hall Effect magnetometer, NMR magnetometer, fluxgate magnetometer are some examples of magnetometers.

Hall Effect is a method used to determine the number density of the carrier and the types of carrier. When the magnetic field is applied perpendicular to the conductor, voltage is set up in the conductor that is perpendicular to the magnetic field as well as the current.

Gouy Balance is a traditional method used to find out the magnetic susceptibility of the material that is based on the idea of gravity.

## How to calculate magnetic field strength in the solenoid that is 5 m long and has 2000 loops, carrying a current of 2000A?

First, find out the number of loops per unit length of the wire

Number of loops per unit length

=Number of loops/Length of wire

=2000/500

=4cm-1

$No.\ of\ loops\ per\ unit\ length \\ \\= \frac{No.\ of\ loops}{Length\ of\ the\ wire} \\ \\ =\frac{2000}{500}=4cm^{-1}$

$Magnetic\ field\ strength\ inside\ the\ solenoid\ B\\ =\mu NI\\=4\Pi \times 10^{-7} T\frac{m}{A}\times 2000\times 400\\=1.01\ Tesla$

## Does the magnetic field strength depend on the size of the conductor?

Yes, as per the Biot – Savart’s Law $B=I\int dl$ magnetic field depends upon the unit length of the conductor. The bigger the size of the conductor, the integral value of the infinitesimal length will be greater, and hence the magnetic field intensity will be higher.

## If the current flowing in two different circuits is 1A and 12A, then in which circuit magnetic strength will be higher than the other?

The magnetic strength will be higher for a circuit carrying current 12A.

## What is Superconducting magnetic material?

A superconducting magnet is used to create an intense magnetic field.

Superconducting magnetic material is an electromagnet made up of a coil of a superconducting wire manufactured at low temperatures. At its superconducting state, the wire has no resistance and conducts a much higher electric current.

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