Magnetic Field - Definition, Formula, Diagram, Properties, FAQs

What is a Magnetic field?

Magnetic fields are defined as the area around a magnet where the influence of the magnet can be felt. It has both magnitude and direction, and the magnetic field, as well as its field and direction, are represented by magnetic field lines.

S.I. Unit of Magnetic field is Tesla (T). and it is represented by B.

History of Magnetic Field

1. The study of magnetism began thousands of years ago when people discovered naturally magnetized stones called lodestones.
2. The ancient Greeks and Chinese noticed that these stones could attract iron and always point in a particular direction when allowed to move freely.
3. Around the 11th century, the Chinese used lodestones to make the first magnetic compasses for navigation.
4. In the 17th century, William Gilbert, an English scientist, proved that the Earth itself acts like a giant magnet.
5. Later, in the 19th century, Hans Christian Ørsted discovered that electric current produces a magnetic field.
6. This led to the development of electromagnetism, further explained by James Clerk Maxwell, who united electricity and magnetism into one theory.

What are Magnetic Field Lines?

Magnetic field lines are imaginary lines that encircle a magnet. The density of a field's line indicates its magnitude. The magnetic field is strongest around the Poles of a magnet and weakens as it goes away from the poles.

Experiment to Observe Magnetic Field

A simple experiment can help to clarify the concept of magnetic field lines. Fix a sheet of white paper to a table and centre it with a bar magnet. Iron filings should be sprinkled around the magnet. Tap the table gently. It can be seen that the iron filings align in a certain pattern that represents the magnet's field. When these patterns are well examined, it is possible to see that iron filings collect around the poles, but the concentration is lower in the region away from the poles.

Magnetic Field Intensity

Magnetic field intensity is a measure of the strength of a magnetic field at a given point. It indicates how strongly a magnetic field can magnetise a material placed in it. It is denoted by H and is a vector quantity, having both magnitude and direction. The SI unit of magnetic field intensity is ampere per meter (A/m). Its direction is the same as that of the magnetic field lines. The magnetic flux density $B$ is related to magnetic field intensity $H$ by the formula:

$
B=\mu H
$

where $\mu$ is the magnetic permeability of the material.

How is Magnetic Field Created?

A magnetic field can be produced not just by a magnet, but also by a moving charge or electric current. We are all aware that matter is made up of small bits known as atoms. An atom's nucleus is made up of protons and neutrons, with electrons orbiting around it. The magnetic field is created by the spinning and circling of protons and neutrons or the nucleus of an atom. The magnetic field's direction is determined by the orbit and spin directions.

Properties of Magnetic Field Lines

1. Magnetic field lines never cross each other.

2. It follows the path with the least resistance between the opposing magnetic poles. A bar magnet's magnetic lines of force travel in closed loops from one pole to the other.

3. The density of the field lines decreases as they pass from the higher permeability region to the lower permeability region.

4. Lines travel from the south pole to the north pole within a material magnetic field, while in the air, they flow from the north pole to the south pole.

5. The density of the magnetic field varies with distance from the pole. Their density reduces as one moves away from the pole.

6. Because it has both magnitude and direction, the magnetic field is a vector quantity.

Properties of Earth's Magnetic Field

1. The magnetic field of the Earth is uniform.

2. The magnetic field strength at the earth's surface is about 10^-4 Tesla.

3. The earth's magnetic field extends up to a height of 5 times the radius of the earth.

Uses of Magnetic Field

Magnetic fields have numerous applications in everyday life, industry, and technology. Some of the important uses are as follows:

Electromagnets
Magnetic fields are used to produce electromagnets, which can be turned on or off by controlling the electric current. Electromagnets are commonly employed in cranes for lifting heavy iron and steel objects.

Electric Motors and Generators
In electric motors, magnetic fields are used to convert electrical energy into mechanical energy. Conversely, generators utilize magnetic fields to convert mechanical energy into electrical energy through electromagnetic induction.

Transformers
Magnetic fields enable transformers to transfer electrical energy from one circuit to another efficiently, without any direct connection, by means of electromagnetic induction.

Magnetic Storage Devices
Data storage devices such as hard disks, tapes, and credit cards make use of magnetic fields to store information reliably.

Medical Applications
Magnetic fields are employed in medical imaging techniques such as Magnetic Resonance Imaging (MRI), which provides detailed internal images of the human body without using harmful radiation.